It only cancels the attached stop once that partial is hit. But I think I get that DAS doesn't have that capability.
Buy 1000 shares of ZZZ
instantly executes and places orders as such....
333 PT 1 and bracketed stop of 333 .50c
333 PT 2 and bracketed stop of 333 .50c
334 PT 3 and bracketed stop of 334 .50c
So if it hits the first it will cancel the corresponding stop, then if it reverses the stop on the other 2 are hit and you're all out.