I had an issue with it too and bug reported it, but my situation was slightly different.
I play with my wife, so after the siege I was stuck on the siege weapon, on my screen, but when I looked at her screen I was actually moving. The mouse turn only turned the siege weapon so I had to keyboard turn and navigate my character looking at my wife's screen and ignoring mine, to the rest of the battle.
I got to complete the instance, but it's definitely bugged.
Had this too and filed a bug report, never sure whether too or not with stuff like that because it might of only been a one time thing and dont want to waste arenanets time but apparently it's a bug then :P
I think I fixed it by going to the map then going off again but the game crashed shortly after.