During Dorn quest where you fight the group of paladins of Tyr(Hammer something). One of the lines Dorn says is said in Ur-Gothoz's voice, very fun and maybe could not be called a bug but more like an error(?) when it was recorded and implemented.
Can't post the audio for reasons but here is a picture of the dialogue. The bugged line is the second one where he says: "I assumed it was your doing".