Yep, agreed that the mindflayer always went hostile if there were no other enemies around. Though in my new playthrough Commander Zhalk wiped him out when I'd only just got to the top of the stairs near them. I wondered if the balance of this battle had been changed again, but sounds like I (or he) was just unlucky with the rolls.

"You may call it 'nonsense' if you like, but I've heard nonsense, compared with which that would be as sensible as a dictionary!"