The transition, in the area with the mithril halls entrance, thatleading deeper into the underdark works when one goes from the mithril area into the next, but one can not to back again.
This was brought up in another report I think, but some in the group thought it had been fixed, so I figured I'd report this one. I apologize if you know its broken and just haven't gotten in the update yet.
Harlas