The RDF is supposed to send you to different portions of the depths depending on the party level and/or variation in the random dungeon finder. However, currently it sends you to the entrance of Molten Core no matter which variation of the dungeon you actually should get. Due to this it's actually impossible to do the Prison portion of the dungeon, which is the lower level portion (making this a very awkward leveling point for players as Blackrock Depths makes up no less than 3 of the RDF possibilities). You can't do the prison section because you cannot enter the lower half of the map from the Molten Core starting point (there's a door that just won't open from this side).
RDF REWARD PROBLEMS
Furthermore, the dungeon is not awarding a satchel, gold, or experience points for its completion. In essence, it's not validating the completion at all. Thus you get stuck in Blackrock depths until you leave the party and get the dungeon deserter debuff which forces you out of the ques for half an hour. On very rare occasions I've heard you do get the reward (I think this may only occur if the RDF intends to send you to the upper city to kill the emperor, as opposed to the other 2 possible portions it intends to send you to).
This dungeon is actually comprised of 2 portions, and you're supposed to be able to complete the RDF objective twice per dungeon if you kill both High Interrogator Gerstahn and the Emperor.
IN SUMMARYDetention Block (Lower City) - 47-57
To complete the Detention Block, you go straight forward into a large open cavern, then turn right into the cell blocks, and kill High Interrogator Gerstahn at the end of the hallway. She is the boss who drops the Satchel. It's a rather quick trip.
Upper City - 51-61
To complete the Upper City, you have to kill the Emperor. This journey will take quite some time due to BRD's size.
If you have already killed the High Interrogator Gerstahn, you will not get the Satchel on killing the Emperor; you will instead get it by mail.
1) Blackrock Depths - Prison is impossible to complete via RDF without the party wiping and entering it manually.
2) Blackrock Depths - Is sending you to the wrong entrance (it's sending you to Molten Core, which is probably the correct one for Upper City but not others).
3) Blackrock Depths - Is not awarding a completion upon killing the Emperor (or theoretically the prison), and thus grants no XP, money, or satchel, or the completion allowing you to leave the party without getting the dungeon deserter debuff.
Here's the WoWwiki link verifying the bugs.