Has anyone else had trouble with quests where you have to Use X, which summons X boss that you then have to defeat? My experience was in the Celestia quest Inevitable Betrayal, where you have to use a pedestal, which summons the creature version of Karolak Nightspinner, who you then have to defeat. I was questing with two other people, and they both sped through the dialogue and used the pedestal before I finished talking to Karolak, summoning him and drawing me into battle. We defeated him, and I noticed my quest arrow said to use a pedestal. Basically, the fact that a boss can be summoned before all players who entered on the sigil complete a required action causes problems. I had to fight that boss again. A similar thing happened with one of the bosses in Grizzleheim, but I can't remember which.
Yeah, a similar thing can happen when you free the Gurtok Barrier Demon in Ravenscar, if the battle is started by someone before you have a chance to use the Brazier.