I'm pretty sure I saw this somewhere already, but couldn't find the thread.  So I'm reporting it again.

I just played a game of Sedna (me) vs Oak (nightmare AI), and especially towards the end my yetis started to behave very stupidly.  They will very easily forget the enemy DG if he walks away, sometimes even when the enemy is still there - whereas my own DG will eagerly follow the enemy right up to the health crystal, and sometimes needs several clicks on the ground to turn back.  A few times when I had both my DG and the yetis selected, they would just stand there until I selected only the yetis and gave them a command.  And at least once I saw them stuck walking against the invisible wall at one of the holes in the map, requiring me to manually guide them around it.

I don't think I saw this bad behaviour in 2C.  Or maybe it's the nightmare AI one way or another?  I haven't played a lot against those.