Gun fort action freeze bug?

I have been able to replicate this one twice post patch 1.02 so I am wondering if other people have witnessed something similar.

If defending in a fort against a direct attack (rather than intercepting) one gets to deploy field defenses. Twice, after I have deployed the pre-battle defenses, when I start moving my units away from the stakes at the start of the battle all of them (even the ones that did not deploy anything) have a weird formation disruption whereby in the middle of the unit there is a big hole. All units seem to have difficulty 'walking around the hole'. As the timer progresses, the non-responsiveness and formation disruption seems to get progressively worse.

What's more interesting (and disrupting) is that the AI attacker walks up to the fort and then just freezes: no action whatsoever neither forward nor backwards. I cannot say the game is completely frozen though since I can still interact with my units. Simply I cannot align them properly anywhere while the AI troops just sit outside near my walls.

Weird.