Let me get this straight...you are the buyer , who has a mortgage in pplace, but are still waiting for the SELLERS bank to approve the short sale and your offer on the property?
That puts another spin on the problem. The SELLERS bank can take up to 6 months (tho not the norm) to approve a short sale and the offer you made. There is a new law in effect that makes the banks have to answer within 30 days UNLESS there is missing paperwork, or they need additional paperwork. They don't have to answer until the packet is complete.
The SELLERS bank can accept, reject or counter-offer your contract as well. I would have your agent speak to the sellers agent to find out if the bank does indeed have ALL the paperwork for the bank's loss mitigation people to make a decision on your offer. I can't stress this enough, missing or incomplete paperwork can delay the process substantially.
Once the bank actually approves the short sale and your offer, typically they give up to 45 days to get your final mortgage commitment and close...the old wait.. wait.. now hurry up routine.