I've found a bug in DropTarget widget, here is an example of this behaviour: http://dojo.telerik.com/eGAFO/2 (check console)
To reproduce this bug you need to create both dropTarget and dropTargetArea inside the container and then do kendo.destroy on the container.
The issue is in destroy method of DropTarget widget, it checks either dropTarget or dropTargetArea internal list, but should check both of them. In my example I have one dropTarget and one dropTargetArea, and code removes group when destroying dropTarget even if dropTargetArea with this group still exists.
To reproduce this bug you need to create both dropTarget and dropTargetArea inside the container and then do kendo.destroy on the container.
The issue is in destroy method of DropTarget widget, it checks either dropTarget or dropTargetArea internal list, but should check both of them. In my example I have one dropTarget and one dropTargetArea, and code removes group when destroying dropTarget even if dropTargetArea with this group still exists.