Actually I too have started to experience this quite often lately. No assigns, nothing at all binding the drawer (or so it seems), but until I have rebooted the system the drawer will fail to be deleted (and sometimes I have even had problems rewing certain drawers after rebooting, although more seldom).
Something has made the system behave like this, because I did not experience this as often before, but I have not clue as of what could be the reason.
