Google trading goes nuts at the end o' the day

Checking my portfolio this afternoon, I noticed Google (NASDAQ:GOOG) had dropped 80 points in the last few minutes of trading! MarketWatch reports that NASDAQ is canceling certain bizarre Google trades:

Nasdaq said Tuesday afternoon that it has cancelled certain trades made on shares of Google Inc. (320.50-60.50-15.88% 5:39pm 09/30/2008 minutes before the closing bell Tuesday. In a statement, the exchange said it will cancel all trades on the stock at or above $425.29 and at or below $400.52 that were executed between 3:57 and 4:02 Eastern. The exchange also said it will be adjusting the Nasdaq Official Closing Cross (NOCP) and all trades executed in the cross to $400.52. The decision came after data late in the trading session seemed to indicate that shares of Google - which were trading up about 8% for most of the session - fell between 10-16% in the final minutes before the closing bell. The statement from Nasdaq did not gie [sic] a reason for the other trades.

Only three letters suffice: WTF? Here's the latest chart from Yahoo.

It shows after-hours trading occurring at $411, which seems a bit more like it.

Of course: what the heck really happened?