I'm not a professional but I've had my own experience with a short sale. In our situation, the homeowner accepted our offer and of course we had to wait on the bank to accept as well. Within 3 days of the homeowners acceptance the listing agent took the home off the market. I was worried about the same thing(signing with someone else as well as us) and my realtor told me that our contract was binding and they could not sign with anyone else. They didn't and looking back now that should've been the last of our worries. It took the bank 3(and might I add LONG) months to even respond to us and when they did they said they accepted our offer but only gave us 2 weeks to close because the house had not paid property taxes in 3 years and the house was about to go back for that. I was already pre-approved through Country Wide but they said they could not get it closed in time due to their underwriters being months behind. So at the last minute I had to switch lenders. The listing agent recommended Mac-Clair Mortgage(just a local company here in Flint, MI). They actually got it done, we closed 1 day before the deadline.
So anyway, I'm not quite sure how they are in Murfreesboro, TN but around here they don't accept multiple offers in a short sale after the homeowner accepted. But the moral to my story is.....make sure your financing is all in order and ready to go because when the bank accepts the offer you don't have much time for whatever reason, in my situation was property taxes. If I wouldn't have found the wonderful people at Mac-Claire Mortgage I would have lost my dream house.
I hope I helped even a little bit, I do know how frustrating and confusing this(short sale process) all could be for you.
If you have any questions don't hesitate to ask, I'm no professional, I can only go by personal experience.