Lee is more or less correct - the "overnight" price jumps that you might be seeing happen, but are atypical.
You're correct on the short sale idea - it's very common for sellers to try and grab lightning, also a waste of time. FNMA and lender owned properties are being listed higher than in the past but I wouldn't call them "overnight" price bumps.
Last - many of the prices you might be seeing may be bait; designed to generate a multiple offer situation. Bottom line is get aligned with an experienced agent that can cut through the BS - like Lee or myself -