gwt drag and drop problem

hello guys,
currently i am working on a project and in that project we are using drag and drop functionality..we are using drag and drop 2.6.2 jar..I have a problem using the drag and drop functionality...
The problem is:-
I have 2 vertical Panel registered to the drop controllers which is IndexedDropController...
These two drop controllers are registered to the drag controller which is PickupDragController...
whenever I drag my draggable item from one vertical panel to another it works fine...
but when i move my draggable item outside the draggable area it hangs there...
I want to restrict the user from dragging outside the absolute panel which contains both the vertical panels..

can anyone help how to restrict dragging outside the absolute panel...