Guild Wars 2

I was on the broken part of the wall destroying enemy catapults when the enemy gained control of the keep, thereby fixing the wall immediately, trapping me inside it.

Getting locked in the wall happens all the time. Same thing happens if your in a gate when possession flips. I normally just waypoint out if not in combat and die if in combat. If friendly mesmer is around sometimes they can get you out by laying a portal on the wall/gate.