Any way you could add a drag cancel event to UICamera line 941 (code below is post-modified code):
This lets the original control who started the drag to receive an event when a drop occurs over a non-collider. If this isn't correct, it would be great to have the correct implementation. For now, it seems to be working fine for me. I am using 2.08 I believe.
else // The button/touch was released on a different object
{
// Send a drop notification (for drag & drop)
if (currentTouch.current != null)
currentTouch.current.SendMessage("OnDrop", currentTouch.pressed, SendMessageOptions.DontRequireReceiver);
// Send a drag cancel event to the control that started the drop since we are dropping on a non-collider (i.e. empty space).
else
currentTouch.pressed.SendMessage("OnDragCancel", SendMessageOptions.DontRequireReceiver);
}