Looks like disabling the formation in the camp menu very sadly does not have an impact on the AI, only on your own troops.
After re-enlisting into a lord army, we got a big battle with another lord, and both armies main strategy was : "we must stay in line formation forever".
The battle summary :
- Let's all move in a line formation
- Attack after waiting for a few minutes
- Contact ! battle finally !
- 5 seconds later, both side retreat a bit, because the battle was starting to break their oh so beloved line formation
- once back into line formation ... attack !
- 5 seconds later, "line formation not perfect ! retreat !"
- once line formation perfect again ... attack !
repeat for more than 10 minutes.
I had ceased to watch, moved my character back to the start point, and was browsing the net while waiting for this to end.
After 20 minutes i ceased to hear the constant warcries, so i went back and noticed it was still not ended.. but there was none fighting anymore.
Quickly checking at the map i noticed why it wasn't finished.
Same problem i reported before, in one of the corner a few troops were running insanely fast , bumping forward and back against a map border.
Probably the AI fleeing code that does not work in Brytenwalda.
Oh well, time to press TAB and retreat as trying to catch those is impossible at the speed they're running.