diff --git a/common/models/change.js b/common/models/change.js
index 572ed43f..afd6625d 100644
--- a/common/models/change.js
+++ b/common/models/change.js
@@ -126,7 +126,7 @@ module.exports = function(Change) {
           modelId: modelId
         });
         ch.debug('creating change');
-        ch.save(callback);
+        Change.updateOrCreate(ch, callback);
       }
     });
   };
@@ -248,6 +248,7 @@ module.exports = function(Change) {
    */
 
   Change.revisionForInst = function(inst) {
+    assert(inst, 'Change.revisionForInst() requires an instance object.');
     return this.hash(CJSON.stringify(inst));
   };
 
@@ -370,15 +371,18 @@ module.exports = function(Change) {
     this.find({
       where: {
         modelName: modelName,
-        modelId: {inq: modelIds},
-        checkpoint: {gte: since}
+        modelId: {inq: modelIds}
       }
-    }, function(err, localChanges) {
+    }, function(err, allLocalChanges) {
       if (err) return callback(err);
       var deltas = [];
       var conflicts = [];
       var localModelIds = [];
 
+      var localChanges = allLocalChanges.filter(function(c) {
+        return c.checkpoint >= since;
+      });
+
       localChanges.forEach(function(localChange) {
         localChange = new Change(localChange);
         localModelIds.push(localChange.modelId);
@@ -396,9 +400,20 @@ module.exports = function(Change) {
       });
 
       modelIds.forEach(function(id) {
-        if (localModelIds.indexOf(id) === -1) {
-          deltas.push(remoteChangeIndex[id]);
+        if (localModelIds.indexOf(id) !== -1) return;
+
+        var d = remoteChangeIndex[id];
+        var oldChange = allLocalChanges.filter(function(c) {
+          return c.modelId === id;
+        })[0];
+
+        if (oldChange) {
+          d.prev = oldChange.rev;
+        } else {
+          d.prev = null;
         }
+
+        deltas.push(d);
       });
 
       callback(null, {
diff --git a/lib/persisted-model.js b/lib/persisted-model.js
index 35c60a84..b33a0cb0 100644
--- a/lib/persisted-model.js
+++ b/lib/persisted-model.js
@@ -952,7 +952,20 @@ function tryReplicate(sourceModel, targetModel, since, options, callback) {
   function bulkUpdate(_updates, cb) {
     debug('\tstarting bulk update');
     updates = _updates;
-    targetModel.bulkUpdate(updates, cb);
+    targetModel.bulkUpdate(updates, function(err) {
+      var conflicts = err && err.details && err.details.conflicts;
+      if (conflicts && err.statusCode == 409) {
+        diff.conflicts = conflicts;
+        // filter out updates that were not applied
+        updates = updates.filter(function(u) {
+          return conflicts
+            .filter(function(d) { return d.modelId === u.change.modelId; })
+            .length === 0;
+        });
+        return cb();
+      }
+      cb(err);
+    });
   }
 
   function checkpoints() {
@@ -974,7 +987,7 @@ function tryReplicate(sourceModel, targetModel, since, options, callback) {
 
     debug('\treplication finished');
     debug('\t\t%s conflict(s) detected', diff.conflicts.length);
-    debug('\t\t%s change(s) applied', updates && updates.length);
+    debug('\t\t%s change(s) applied', updates ? updates.length : 0);
     debug('\t\tnew checkpoints: { source: %j, target: %j }',
       newSourceCp, newTargetCp);
 
@@ -1058,31 +1071,197 @@ PersistedModel.createUpdates = function(deltas, cb) {
 PersistedModel.bulkUpdate = function(updates, callback) {
   var tasks = [];
   var Model = this;
-  var idName = this.dataSource.idName(this.modelName);
   var Change = this.getChangeModel();
+  var conflicts = [];
 
-  updates.forEach(function(update) {
-    switch (update.type) {
-      case Change.UPDATE:
-      case Change.CREATE:
-        // var model = new Model(update.data);
-        // tasks.push(model.save.bind(model));
-        tasks.push(function(cb) {
-          var model = new Model(update.data);
-          model.save(cb);
-        });
-        break;
-      case Change.DELETE:
-        var data = {};
-        data[idName] = update.change.modelId;
-        var model = new Model(data);
-        tasks.push(model.destroy.bind(model));
-        break;
+  buildLookupOfAffectedModelData(Model, updates, function(err, currentMap) {
+    if (err) return callback(err);
+
+    updates.forEach(function(update) {
+      var id = update.change.modelId;
+      var current = currentMap[id];
+      switch (update.type) {
+        case Change.UPDATE:
+          tasks.push(function(cb) {
+            applyUpdate(Model, id, current, update.data, update.change, conflicts, cb);
+          });
+          break;
+
+        case Change.CREATE:
+          tasks.push(function(cb) {
+            applyCreate(Model, id, current, update.data, update.change, conflicts, cb);
+          });
+          break;
+        case Change.DELETE:
+          tasks.push(function(cb) {
+            applyDelete(Model, id, current, update.change, conflicts, cb);
+          });
+          break;
+      }
+    });
+
+    async.parallel(tasks, function(err) {
+      if (err) return callback(err);
+      if (conflicts.length) {
+        err = new Error('Conflict');
+        err.statusCode = 409;
+        err.details = { conflicts: conflicts };
+        return callback(err);
+      }
+      callback();
+    });
+  });
+};
+
+function buildLookupOfAffectedModelData(Model, updates, callback) {
+  var idName = Model.dataSource.idName(Model.modelName);
+  var affectedIds = updates.map(function(u) { return u.change.modelId; });
+  var whereAffected = {};
+  whereAffected[idName] = { inq: affectedIds };
+  Model.find({ where: whereAffected }, function(err, affectedList) {
+    if (err) return callback(err);
+    var dataLookup = {};
+    affectedList.forEach(function(it) {
+      dataLookup[it[idName]] = it;
+    });
+    callback(null, dataLookup);
+  });
+}
+
+function applyUpdate(Model, id, current, data, change, conflicts, cb) {
+  var Change = Model.getChangeModel();
+  var rev = current ?  Change.revisionForInst(current) : null;
+
+  if (rev !== change.prev) {
+    debug('Detected non-rectified change of %s %j',
+      Model.modelName, id);
+    debug('\tExpected revision: %s', change.rev);
+    debug('\tActual revision:   %s', rev);
+    conflicts.push(change);
+    return Change.rectifyModelChanges(Model.modelName, [id], cb);
+  }
+
+  // TODO(bajtos) modify `data` so that it instructs
+  // the connector to remove any properties included in "inst"
+  // but not included in `data`
+  // See https://github.com/strongloop/loopback/issues/1215
+
+  Model.updateAll(current.toObject(), data, function(err, result) {
+    if (err) return cb(err);
+
+    var count = result && result.count;
+    switch (count) {
+      case 1:
+        // The happy path, exactly one record was updated
+        return cb();
+
+      case 0:
+        debug('UpdateAll detected non-rectified change of %s %j',
+          Model.modelName, id);
+        conflicts.push(change);
+        // NOTE(bajtos) updateAll triggers change rectification
+        // for all model instances, even when no records were updated,
+        // thus we don't need to rectify explicitly ourselves
+        return cb();
+
+      case undefined:
+      case null:
+        return cb(new Error(
+          'Cannot apply bulk updates, ' +
+          'the connector does not correctly report ' +
+          'the number of updated records.'));
+
+      default:
+        debug('%s.updateAll modified unexpected number of instances: %j',
+          Model.modelName, count);
+        return cb(new Error(
+          'Bulk update failed, the connector has modified unexpected ' +
+          'number of records: ' + JSON.stringify(count)));
     }
   });
+}
 
-  async.parallel(tasks, callback);
-};
+function applyCreate(Model, id, current, data, change, conflicts, cb) {
+  Model.create(data, function(createErr) {
+    if (!createErr) return cb();
+
+    // We don't have a reliable way how to detect the situation
+    // where he model was not create because of a duplicate id
+    // The workaround is to query the DB to check if the model already exists
+    Model.findById(id, function(findErr, inst) {
+      if (findErr || !inst) {
+        // There isn't any instance with the same id, thus there isn't
+        // any conflict and we just report back the original error.
+        return cb(createErr);
+      }
+
+      return conflict();
+    });
+  });
+
+  function conflict() {
+    // The instance already exists - report a conflict
+    debug('Detected non-rectified new instance of %s %j',
+      Model.modelName, id);
+    conflicts.push(change);
+
+    var Change = Model.getChangeModel();
+    return Change.rectifyModelChanges(Model.modelName, [id], cb);
+  }
+}
+
+function applyDelete(Model, id, current, change, conflicts, cb) {
+  if (!current) {
+    // The instance was either already deleted or not created at all,
+    // we are done.
+    return cb();
+  }
+
+  var Change = Model.getChangeModel();
+  var rev = Change.revisionForInst(current);
+  if (rev !== change.prev) {
+    debug('Detected non-rectified change of %s %j',
+      Model.modelName, id);
+    debug('\tExpected revision: %s', change.rev);
+    debug('\tActual revision:   %s', rev);
+    conflicts.push(change);
+    return Change.rectifyModelChanges(Model.modelName, [id], cb);
+  }
+
+  Model.deleteAll(current.toObject(), function(err, result) {
+    if (err) return cb(err);
+
+    var count = result && result.count;
+    switch (count) {
+      case 1:
+        // The happy path, exactly one record was updated
+        return cb();
+
+      case 0:
+        debug('DeleteAll detected non-rectified change of %s %j',
+          Model.modelName, id);
+        conflicts.push(change);
+        // NOTE(bajtos) deleteAll triggers change rectification
+        // for all model instances, even when no records were updated,
+        // thus we don't need to rectify explicitly ourselves
+        return cb();
+
+      case undefined:
+      case null:
+        return cb(new Error(
+          'Cannot apply bulk updates, ' +
+          'the connector does not correctly report ' +
+          'the number of deleted records.'));
+
+      default:
+        debug('%s.deleteAll modified unexpected number of instances: %j',
+          Model.modelName, count);
+        return cb(new Error(
+          'Bulk update failed, the connector has deleted unexpected ' +
+          'number of records: ' + JSON.stringify(count)));
+    }
+  });
+}
 
 /**
  * Get the `Change` model.
diff --git a/test/change.test.js b/test/change.test.js
index 74055b52..02a059df 100644
--- a/test/change.test.js
+++ b/test/change.test.js
@@ -1,4 +1,5 @@
 var async = require('async');
+var expect = require('chai').expect;
 
 var Change;
 var TestModel;
@@ -134,11 +135,16 @@ describe('Change', function() {
 
   describe('change.rectify(callback)', function() {
     var change;
-    beforeEach(function() {
-      change = new Change({
-        modelName: this.modelName,
-        modelId: this.modelId
-      });
+    beforeEach(function(done) {
+      Change.findOrCreate(
+        {
+          modelName: this.modelName,
+          modelId: this.modelId
+        },
+        function(err, ch) {
+          change = ch;
+          done(err);
+        });
     });
 
     it('should create a new change with the correct revision', function(done) {
@@ -344,10 +350,89 @@ describe('Change', function() {
       ];
 
       Change.diff(this.modelName, 0, remoteChanges, function(err, diff) {
+        if (err) return done(err);
         assert.equal(diff.deltas.length, 1);
         assert.equal(diff.conflicts.length, 1);
         done();
       });
     });
+
+    it('should set "prev" to local revision in non-conflicting delta', function(done) {
+      var updateRecord = {
+        rev: 'foo-new',
+        prev: 'foo',
+        modelName: this.modelName,
+        modelId: '9',
+        checkpoint: 2
+      };
+      Change.diff(this.modelName, 0, [updateRecord], function(err, diff) {
+        if (err) return done(err);
+        expect(diff.conflicts, 'conflicts').to.have.length(0);
+        expect(diff.deltas, 'deltas').to.have.length(1);
+        var actual = diff.deltas[0].toObject();
+        delete actual.id;
+        expect(actual).to.eql({
+          checkpoint: 2,
+          modelId: '9',
+          modelName: updateRecord.modelName,
+          prev: 'foo', // this is the current local revision
+          rev: 'foo-new',
+        });
+        done();
+      });
+    });
+
+    it('should set "prev" to local revision in remote-only delta', function(done) {
+      var updateRecord = {
+        rev: 'foo-new',
+        prev: 'foo-prev',
+        modelName: this.modelName,
+        modelId: '9',
+        checkpoint: 2
+      };
+      // IMPORTANT: the diff call excludes the local change
+      // with rev=foo CP=1
+      Change.diff(this.modelName, 2, [updateRecord], function(err, diff) {
+        if (err) return done(err);
+        expect(diff.conflicts, 'conflicts').to.have.length(0);
+        expect(diff.deltas, 'deltas').to.have.length(1);
+        var actual = diff.deltas[0].toObject();
+        delete actual.id;
+        expect(actual).to.eql({
+          checkpoint: 2,
+          modelId: '9',
+          modelName: updateRecord.modelName,
+          prev: 'foo', // this is the current local revision
+          rev: 'foo-new',
+        });
+        done();
+      });
+    });
+
+    it('should set "prev" to null for a new instance', function(done) {
+      var updateRecord = {
+        rev: 'new-rev',
+        prev: 'new-prev',
+        modelName: this.modelName,
+        modelId: 'new-id',
+        checkpoint: 2
+      };
+
+      Change.diff(this.modelName, 0, [updateRecord], function(err, diff) {
+        if (err) return done(err);
+        expect(diff.conflicts).to.have.length(0);
+        expect(diff.deltas).to.have.length(1);
+        var actual = diff.deltas[0].toObject();
+        delete actual.id;
+        expect(actual).to.eql({
+          checkpoint: 2,
+          modelId: 'new-id',
+          modelName: updateRecord.modelName,
+          prev: null, // this is the current local revision
+          rev: 'new-rev',
+        });
+        done();
+      });
+    });
   });
 });
diff --git a/test/replication.test.js b/test/replication.test.js
index 8bf5dcbd..6c875d25 100644
--- a/test/replication.test.js
+++ b/test/replication.test.js
@@ -88,12 +88,10 @@ describe('Replication / Change APIs', function() {
       var targetData;
 
       this.SourceModel.create({name: 'foo'}, function(err) {
-        setTimeout(replicate, 100);
-      });
-
-      function replicate() {
+        if (err) return done(err);
         test.SourceModel.replicate(test.startingCheckpoint, test.TargetModel,
         options, function(err, conflicts) {
+          if (err) return done(err);
           assert(conflicts.length === 0);
           async.parallel([
             function(cb) {
@@ -117,7 +115,7 @@ describe('Replication / Change APIs', function() {
             done();
           });
         });
-      }
+      });
     });
 
     it('applies "since" filter on source changes', function(done) {
@@ -179,18 +177,11 @@ describe('Replication / Change APIs', function() {
     });
 
     it('picks up changes made during replication', function(done) {
-      var bulkUpdate = TargetModel.bulkUpdate;
-      TargetModel.bulkUpdate = function(data, cb) {
-        var self = this;
+      setupRaceConditionInReplication(function(cb) {
         // simulate the situation when another model is created
         // while a replication run is in progress
-        SourceModel.create({ id: 'racer' }, function(err) {
-          if (err) return cb(err);
-          bulkUpdate.call(self, data, cb);
-        });
-        // create the new model only once
-        TargetModel.bulkUpdate = bulkUpdate;
-      };
+        SourceModel.create({ id: 'racer' }, cb);
+      });
 
       var lastCp;
       async.series([
@@ -291,6 +282,128 @@ describe('Replication / Change APIs', function() {
         }
       ], done);
     });
+
+    describe('with 3rd-party changes', function() {
+      it('detects UPDATE made during UPDATE', function(done) {
+        async.series([
+          createModel(SourceModel, { id: '1' }),
+          replicateExpectingSuccess(),
+          function updateModel(next) {
+            SourceModel.updateAll({ id: '1' }, { name: 'source' }, next);
+          },
+          function replicateWith3rdPartyModifyingData(next) {
+            setupRaceConditionInReplication(function(cb) {
+              TargetModel.dataSource.connector.updateAttributes(
+                TargetModel.modelName,
+                '1',
+                { name: '3rd-party' },
+                cb);
+            });
+
+            SourceModel.replicate(
+              TargetModel,
+              function(err, conflicts, cps, updates) {
+                if (err) return next(err);
+
+                var conflictedIds = getPropValue(conflicts || [], 'modelId');
+                expect(conflictedIds).to.eql(['1']);
+
+                // resolve the conflict using ours
+                conflicts[0].resolve(next);
+              });
+          },
+
+          replicateExpectingSuccess(),
+          verifyInstanceWasReplicated(SourceModel, TargetModel, '1')
+        ], done);
+      });
+
+      it('detects CREATE made during CREATE', function(done) {
+        async.series([
+          // FIXME(bajtos) Remove the 'name' property once the implementation
+          // of UPDATE is fixed to correctly remove properties
+          createModel(SourceModel, { id: '1', name: 'source' }),
+          function replicateWith3rdPartyModifyingData(next) {
+            setupRaceConditionInReplication(function(cb) {
+              TargetModel.dataSource.connector.create(
+                TargetModel.modelName,
+                { id: '1', name: '3rd-party' },
+                cb);
+            });
+
+            SourceModel.replicate(
+              TargetModel,
+              function(err, conflicts, cps, updates) {
+                if (err) return next(err);
+
+                var conflictedIds = getPropValue(conflicts || [], 'modelId');
+                expect(conflictedIds).to.eql(['1']);
+
+                // resolve the conflict using ours
+                conflicts[0].resolve(next);
+              });
+          },
+
+          replicateExpectingSuccess(),
+          verifyInstanceWasReplicated(SourceModel, TargetModel, '1')
+        ], done);
+      });
+
+      it('detects UPDATE made during DELETE', function(done) {
+        async.series([
+          createModel(SourceModel, { id: '1' }),
+          replicateExpectingSuccess(),
+          function deleteModel(next) {
+            SourceModel.deleteById('1', next);
+          },
+          function replicateWith3rdPartyModifyingData(next) {
+            setupRaceConditionInReplication(function(cb) {
+              TargetModel.dataSource.connector.updateAttributes(
+                TargetModel.modelName,
+                '1',
+                { name: '3rd-party' },
+                cb);
+            });
+
+            SourceModel.replicate(
+              TargetModel,
+              function(err, conflicts, cps, updates) {
+                if (err) return next(err);
+
+                var conflictedIds = getPropValue(conflicts || [], 'modelId');
+                expect(conflictedIds).to.eql(['1']);
+
+                // resolve the conflict using ours
+                conflicts[0].resolve(next);
+              });
+          },
+
+          replicateExpectingSuccess(),
+          verifyInstanceWasReplicated(SourceModel, TargetModel, '1')
+        ], done);
+      });
+
+      it('handles DELETE made during DELETE', function(done) {
+        async.series([
+          createModel(SourceModel, { id: '1' }),
+          replicateExpectingSuccess(),
+          function deleteModel(next) {
+            SourceModel.deleteById('1', next);
+          },
+          function setup3rdPartyModifyingData(next) {
+            setupRaceConditionInReplication(function(cb) {
+              TargetModel.dataSource.connector.destroy(
+                TargetModel.modelName,
+                '1',
+                cb);
+            });
+            next();
+          },
+          replicateExpectingSuccess(),
+          verifyInstanceWasReplicated(SourceModel, TargetModel, '1')
+        ], done);
+      });
+    });
   });
 
   describe('conflict detection - both updated', function() {
@@ -878,7 +991,7 @@ describe('Replication / Change APIs', function() {
             function resolveManually(conflict, cb) {
               conflict.models(function(err, source, target) {
                 if (err) return cb(err);
-                var m = new conflict.SourceModel(source || target);
+                var m = source || new conflict.SourceModel(target);
                 m.name = 'manual';
                 m.save(function(err) {
                   if (err) return cb(err);
@@ -897,7 +1010,7 @@ describe('Replication / Change APIs', function() {
         async.series([
           // sync the new model to ClientB
           sync(ClientB, Server),
-          verifyInstanceWasReplicated(ClientA, ClientB),
+          verifyInstanceWasReplicated(ClientA, ClientB, sourceInstanceId),
 
           // ClientA makes a change
           updateSourceInstanceNameTo('a'),
@@ -924,7 +1037,7 @@ describe('Replication / Change APIs', function() {
           // and sync back to ClientA too
           sync(ClientA, Server),
 
-          verifyInstanceWasReplicated(ClientB, ClientA)
+          verifyInstanceWasReplicated(ClientB, ClientA, sourceInstanceId)
         ], cb);
       }
 
@@ -953,6 +1066,7 @@ describe('Replication / Change APIs', function() {
 
     function updateSourceInstanceNameTo(value) {
       return function updateInstance(next) {
+        debug('update source instance name to %j', value);
         sourceInstance.name = value;
         sourceInstance.save(next);
       };
@@ -960,6 +1074,7 @@ describe('Replication / Change APIs', function() {
 
     function deleteSourceInstance(value) {
       return function deleteInstance(next) {
+        debug('delete source instance', value);
         sourceInstance.remove(function(err) {
           sourceInstance = null;
           next(err);
@@ -978,21 +1093,6 @@ describe('Replication / Change APIs', function() {
         });
       };
     }
-
-    function verifyInstanceWasReplicated(source, target) {
-      return function verify(next) {
-        source.findById(sourceInstanceId, function(err, expected) {
-          if (err) return next(err);
-          target.findById(sourceInstanceId, function(err, actual) {
-            if (err) return next(err);
-            expect(actual && actual.toObject())
-              .to.eql(expected && expected.toObject());
-            debug('replicated instance: %j', actual);
-            next();
-          });
-        });
-      };
-    }
   });
 
   var _since = {};
@@ -1021,6 +1121,12 @@ describe('Replication / Change APIs', function() {
     });
   }
 
+  function createModel(Model, data) {
+    return function create(next) {
+      Model.create(data, next);
+    };
+  }
+
   function replicateExpectingSuccess(source, target, since) {
     if (!source) source = SourceModel;
     if (!target) target = TargetModel;
@@ -1037,6 +1143,37 @@ describe('Replication / Change APIs', function() {
     };
   }
 
+  function setupRaceConditionInReplication(fn) {
+    var bulkUpdate = TargetModel.bulkUpdate;
+    TargetModel.bulkUpdate = function(data, cb) {
+      // simulate the situation when a 3rd party modifies the database
+      // while a replication run is in progress
+      var self = this;
+      fn(function(err) {
+        if (err) return cb(err);
+        bulkUpdate.call(self, data, cb);
+      });
+
+      // apply the 3rd party modification only once
+      TargetModel.bulkUpdate = bulkUpdate;
+    };
+  }
+
+  function verifyInstanceWasReplicated(source, target, id) {
+    return function verify(next) {
+      source.findById(id, function(err, expected) {
+        if (err) return next(err);
+        target.findById(id, function(err, actual) {
+          if (err) return next(err);
+          expect(actual && actual.toObject())
+            .to.eql(expected && expected.toObject());
+          debug('replicated instance: %j', actual);
+          next();
+        });
+      });
+    };
+  }
+
   function spyAndStoreSinceArg(Model, methodName, store) {
     var orig = Model[methodName];
     Model[methodName] = function(since) {