Short answer, if you, as the seller, sign a promissory note to pay for the deficiency, then, yes, you are liable for the amount. If the condition of short sale approval is that the seller must agree to pay for the deficiency--then, again, yes, the seller is liable for the amount. However, as the others have noted, there is a huge difference between being liable for the deficiency and being "required" to pay it now. In some cases, banks are agreeing to forego the immediate collection, but I do think that banks are just tricky enough to require that at some point in the future, the money be repaid.
This is why the provisions of the new HAFA (Home Affordable Foreclosure Alternative) program, enacted on April 5, 2010, has, as one of its requirements, a provision that disallows the lender from requiring the seller to be responsible for the deficient amount. In other words, the lender is agreeing, under HAFA to waive collection of any deficiency now and forever. However, HAFA applies ONLY to those short sales after April 5, 2010 (nothing before this date) and sellers must first try to apply for the HAMP program before being allowed to sell short under HAFA. Realtors who attempt to help homeowners with HAMP and HAFA should be trained to do so since the new rules for short sales under HAFA are drastically different than what we've seen in the past and there are specific short and long form applications for HAFA. Talk with a Realtor who has either a CDPE (Certified Distressed Property Expert) or SFR (Short Sale Certification under NAR) to assist you.
If you can qualify to sell the home under HAFA, you need not worry about having to pay for the deficiency in now or in the future.
Grace Morioka, SRES
Area Pro Realty
San Jose, CA