That's true for single-legged positions using the Options window, but when you click on positions in multi-legged trades to close using the Spreads window, the qty is always 1.
It's a PITA as I frequently forget to adjust the qty and either think I've closed the position only to see that I have n-1 remaining, or if I catch it, I have to cancel and resubmit.
I requested that the qty's get transferred; the wrinkle is when all legs aren't the same qty, but Kosta said he might be able to do something for when they are.