It's not just P. Have a look at LNKD, RENN, YOKU (earlier this week), SPRD, and in fact, have a look at SPY: http://www.elitetrader.com/vb/showthread.php?threadid=222976
mkt will do something stupid in both directions 90% of the time. this is why it pays to be just a little retarded to maximize profits.