At times traders/systems make mistakes. Sometimes the mistakes are small and something they are large. Those who might recall, there was a large mistake a while back, that resulted in the infamous "flash-crash".
At times such mistakes are small and hardly get media attention. But such trades result into losses for some, and gains for some. Looks like today a few shares of PSAU were traded at an unusually high price of $26.50. Those who sold (or covered) at this price have lost and those who bought (or shorted) have gained.
Lucky for me that some of my short trades for PSAU went thru at 26.50 today 5/1/2013 around 9:30am Eastern. Meaning I shorted at 26.50. Presently PSAU is trading at 24.72. If I were to cover right away, that would be a gain of more than 6% in a matter of less than 30 minutes.