FWIW I've experienced this same bug a little deeper in the stronghold.
After we talked to the Custodian -- whatever the talking statue up in the main hall is called -- we were able to get past the doorway just off the prison that was previously blocked by the force-field. In there, at the room with the Wyrm, Priests, Champion etc, we got stuck in endless combat too. The enemy were long dead but there was seemingly nothing we could do to get out of combat mode.
I tried everything I could think of but eventually had to abort and quit out of the game to get out of Combat.
I'm on Steam, Linux Mint 17.1.