You need to consult an attorney and read your lease carefully. There are official steps you should take to end the lease and just walking away could still leave you liable for the remaining term of the lease. If they have applied for a short sale their is a good possibility that they are no longer paying the mortgage and your rent is not going towards paying the mortgage on the property you are living in. Document everything and determine whether your rent should be going directly to the landlord or to a third party to hold until the issue is resolved
Short sales can be used for investment property though if the owner is still getting mail at the address they could be claiming it as a primary residence.
Good luck I'm sure this isn't what you were looking forward to when you moved into your new home. - Earlier today