Help with a Drag&Drop App

Help with a Drag&Drop App

Hello,

here is my current project :

http://wir3d.net/tests/drag-drop-resizable/

The main drag & drop works (dragging items from right column to container).

But then, if I drag this instance into its parent, it creates a new instance. I'd like to avoid this endless duplication. Once a item is dropped into the container, it should keep being draggable into the parent, but should't create new instance.

How can I do that ?