The Lake of Sounds isn't considered a "dungeon" or doesn't have the "dungeon logging script". Since there is no way out of that map other than killing the boss, it makes it impossible to leave this map, if something goes wrong and you fail to kill the boss. The only way out is to wait for a server reset to be able to go somewhere else. It also doesn't despawn any mobs that weren't killed the last time someone was there.
Possible solutions: Add the script to allow people to dungeon log from this map, or add a rope back up the map right before, so people can leave the dungeon if things goes wrong in the last room.
