Well in certain cases that is considered "desired behavior" and I can't for the life of me remember/imagine the scenario you are describing but I have had to wrestle with it myself (and it ended up making sense after studying up on the Comping mode) HOWEVER if you are experiencing different behavior while perform the EXACT same moves in another track then perhaps there is a bit of project corruption occurring.
It seems like you have already found a workaround for this particular problem but if not try out the different tools and now I'm going to say even switch to Sound On Sound mode temporarily to stretch the track out.
I will say though that it sounds like you have simply been dragging the wrong part of the clip. Dragging the top middle three quarters of the clip edge vs. the bottom half of the clip edge will either a) crop all other clips in that area along with your crop move or b) leave the other clips alone and allow you to crop the clip by itself.
Sorry... I forget which does which and that may have been confusing but either you are dragging the wrong section or the program is registering your drag move as being applied in the wrong area. No way to know without getting my hands on your mouse and doing it myself.
Cheers.