pass in legacyEvent to eventDrop. fix dateDelta

src/common/Grid.events.js

@@ -372,7 +372,7 @@ Grid.mixin({
 				footprint = hit.component.getSafeHitFootprint(hit);
 
 				if (origFootprint && footprint) {
-					eventDefMutation = _this.computeEventDropMutation(origFootprint, footprint);
+					eventDefMutation = _this.computeEventDropMutation(origFootprint, footprint, event);
 
 					if (eventDefMutation) {
 						mutatedEventInstanceGroup = eventManager.buildMutatedEventInstanceGroup(
@@ -500,7 +500,7 @@ Grid.mixin({
 
 
 	// DOES NOT consider overlap/constraint
-	computeEventDropMutation: function(startFootprint, endFootprint) {
+	computeEventDropMutation: function(startFootprint, endFootprint, legacyEvent) {
 		var date0 = startFootprint.unzonedRange.getStart();
 		var date1 = endFootprint.unzonedRange.getStart();
 		var clearEnd = false;

src/common/View.js

@@ -728,10 +728,11 @@ var View = FC.View = ChronoComponent.extend({
 			eventMutation,
 			this.calendar
 		);
+		var dateMutation = eventMutation.dateMutation;
 
 		this.triggerEventDrop(
 			eventManager.getEventInstancesWithId(eventDef.id)[0].toLegacy(),
-			eventMutation.dateMutation.dateDelta,
+			(dateMutation && dateMutation.dateDelta) || moment.duration(),
 			undoFunc,
 			el, ev
 		);