Units defending walls won't keep their position. They start running toward the enemy once the enemy has breeched the walls. This may be a new feature but it is annoying as hell. The same applies to units defending the courtyard. They also won't keep their position. It may something like "may charge without orders but it is very annoying. Did I say very, well it is very very annoying.

I build a fort to defend Brussels. A nice fort with four corners and a breech in it. There was no message that the building was sabotaged. I captured Brussels without a fort. There was a breech from the start. Bloody Belgians can't build a proper fort.