If you have used two guesting tickets and then try to join a dungeon that is not on your server, you will be punted all the way to desktop. This is for patch 26,0077 (most recent patch as of this posting). Friends are saying this has been happening all day. So, the bug was likely introduced in the initial patch today.
Our group typically has at least one player with two tickets used up. So, this bug essentially makes dungeon play impossible, which is about 90% of the game for us. Our static essentially logged for the night as a result.