Heres a wierd one, I've seen it two or three times now (I'm a 100 turns or more into the campaign, so its not frequent) and thought to take some pictures on the last time I saw it.

I'm sallying out from a castle under siege, and several AI units, before I even give my men any orders immediately make a run for the corner of my city walls.



They remained their unmoving whilst I fought the two units that hadn't gone to admire the masonary.



After I'd routed the half of their force (which behaved normally) one of the three units made a dash for my gate, I blocked its progress but they continued, attempting to simply march straight through my unit.



However I have seen AI units doing this head on so maybe its an unrelated bug - a "corner" bug and a "march to the gate" bug. The other two units back at the corner continued their behaviour however, even as I shot them in the back with crossbow men.