jumping the queue?

I placed a 50,000 AGO sell order @ 80 cents at 1.15pm today. At the time it was trading around 77.5-78.0 cents and there were less than 350,000 shares listed for sale at 80c, including mine.

I had to go out for the afternoon and my order is still listed as open. However over 450,000 shares(excluding cross-trades) were exchanged at 4.10pm at 80 cents which was the only time it hit that price all day.

How does this happen and has anyone else had a similar experience?

I can check in the morning but who should I contact ASX or E*Trade?