Honestly, it probably just means the seller has accepted an offer and now it's going to the bank for review and possible approval of the short sale. There doesn't seem to be any consistent use of the pending statuses PR or PS for short sales.
FYI, per MLS rules "pending release" means the accepted offer is contingent on the sale of the buyer's current property. "Pending show" means the buyer's investigation, appraisal and loan contingencies have not been removed. An offer with "PR" status could be bumped by another buyer if the existing buyer cannot remove the contingency for the sale of their property within 3 days. An offer with "PS" can't be bumped by another buyer.
Hope this helps.