In the Duke's castle, when Seravok's doppelgangers are to attack, if one of the doppelgangers becomes feared it may run upstairs. However, upstairs is inaccessible until all of the doppelgangers are dead.. rendering the game *broken* if one should flee upstairs during this event.
Either these doppelgangers should be immune to fear or the stairs should be accessible by players during this encounter so that all of them may be killed.
The doorway outside to Baldur's Gate is accessible; I don't know if any of the doppelgangers can flee in that direction or what consequences it might have on the game. As it is very difficult to duplicate this, I am uncertain if the game would know if they were all killed if they left the area at all.