I have noticed the braindead AI multiple posts in the feedback roundup. I think the reason might be that every once in a while (frequently though in a battle) the character stops responding (won't attack, won't cast) until given a move order. If the AI is giving commands and the character stops responding, humans know to move the char and it will work, the AI assumes that it works. So the AI's assumption is wrong, and it stands there issuing commands which have no effect. So you wind up with a rook standing there braindead taking a beating.

There is more to the AI, like if it has 100 hp it will charge in head first into the enemy base, but that is a different problem (maybe).