cloning old data before updating to fix #1378

lib/DataSet.js

@@ -243,10 +243,11 @@ DataSet.prototype.update = function (data, senderId) {
   var addOrUpdate = function (item) {
     var id = item[fieldId];
     if (me._data[id]) {
+      var oldData = util.extend({}, me._data[id]);
       // update item
       id = me._updateItem(item);
       updatedIds.push(id);
-      updatedData.push(item);
+      updatedData.push(oldData);
     }
     else {
       // add new item
@@ -513,7 +514,7 @@ DataSet.prototype.forEach = function (callback, options) {
   var filter = options && options.filter,
       type = options && options.type || this._options.type,
       data = this._data,
-      itemIds = Object.key(data),
+      itemIds = Object.keys(data),
       i,
       len,
       item,