I don’t consider it bugged but rather the way they attempted to “fix” the issue in order to re-create the undead-side run is just massively different than how the dungeon worked prior to Cataclysm.
The weird behavior only occurs if you spawn your instance by entering the live side first. When you do this, your instance has been flagged as a “live” run and attempting to zone in to the service entrance will place you back at the live entrance.
Conversely, if you reset your instance and zone in to the service entrance first, then your run is flagged as “undead” and the gate to the live side will remain closed. (I haven’t tested whether zoning out and going back to the live entrance puts you at service in this scenario, but I would assume it does.)
It’d be nice if they just put it back to the way it worked from vanilla through Wrath.