I would not allow them to jerk you around on this. Ask them to file and ask for a copy of the filing and a notification when the court date is sent. You can also attend the court proceeding as it is public. This way you will know exactly what is happening. The reason is that this could effectively stop the process if this is not done. They seller may be trying to see how long they can live for free in the house and they may be using you as a pawn.
If the seller is not willing to cooperate, move on.
For the short sale to go through, you will need to get the approval of the bankruptcy judge to proceed with the sale (or in legal jargon, lift the stay) before the bank can proceed with approving the short sale itself.
The main question you need to have answered is if the seller is still interested in selling the home. If so, the BK is probably just delaying tactic to stay in the house longer rent free and if you are getting a bargain price for it, it may be worth the wait (although at this point, the bank has not really approved the sales price and could come back and ask for more).
As a listing agent I've had this kind of seller tell me that they would instruct their bankruptcy attorney to have the home sale removed by the court from that purview of the bankruptcy. The attorney then wouldn't return my calls, then would maintain that they could not talk to me due to attorney/client confidentiality, then say that the seller never instructed them to do anything about removing the property sale from the purview of the bankruptcy court.
If the seller is sincere about the short sale they can have the sale rapidly removed from bankruptcy court jurisdiction. If they don't do this promptly, they very likely fall into the category of an insincere seller. Your best bet would probably be to move on at that point and attempt to terminate your contractual obligation to the purchase of the property.