I noticed a lot of folks stuck like that in a big kill-all I did on an 8-team in a mission with a million ambushes. At the time, I just chalked it up to there being about 60 or so of them inside of the space of a square block. 
Dec out.
hmm, in my case it was very noticeable with 3 ambushes on a medium sized map (front, mid and back). They were ally ambushes but I suspect that does not make a difference.
I have noticed a lot of my critters (especially patrols and ambushes) getting stuck on tiny rocks in cave maps and things like torches in the CoT maps. Also, a lot of the enemies seem to be "turned off". I can walk right up to them and unless I hit them they ignore me for a long time, which is not good for ranged critters. :P Anyone else having these kind of issues?