The door at the end of Samael's paladin quest would not initiate a conversation with me, yesterday, so I couldn't get it to open. (Then the server reset before I could get a DM to open it for me, and it's a no-repeat quest.)
As cool as the conversation was, if it can't always work then maybe the boss should just drop a key, and a ghost on the other side of the door talks to you for flavor.