jquery/jquery-ui — comment on commit e9f5c1857f9d70e69f08be158b2275736c02647f
File: ui/jquery.ui.droppable.js line 124
By DaveStein:

If user is using draggable with helper and stops propogation of dragStop, the helper stays on screen in place. On mouseup the helper will still be there. Should it count as a drop? If so they should stay separate, otherwise this should definitely go off of dragStop.