Unusual 1-minute bar on QQQ 9-2-11

Maybe a dumb rookie question but I'll ask anyway. On Friday 9-2-11, QQQ traded in a fairly narrow range except for one bar @ 9:39 AM. This bar opened at 53.43, went up to 54.61 and closed at 53.42. Any ideas what would cause this, and would it trigger any open orders above the market? Any thoughts would be much appreciated.

 

Bad tick. Happens once in a while and gets corrected on the charts.

 

Sometimes these "bad" prints are the result of institutional options trades that are paired with the underlying security. Happens ALL day to accommodate the delta neutral options trade.

 

ETFs, always getting these "bad ticks"
SPY, probably the worst
DIA, probably the cleanest

 

Many thanks for the possible scenarios. At least there is now some rationale for why this occurred.