If it is a system mistake, how long does it take them to correct it?
I've been watching for the last couple weeks, since I thought I had a chance of winning one of the investor prizes, and the same thing happened this monday (April 21st). Maybe people showed up out of nowhere (not in the top 25 of the previous day), so that they must have had less than $145K. Then on monday, they showed up with gains of at least $50K to $150K in one day, and none of those people have disappeared yet. (opp36467, bryant04, Seraphim, tcushing, winkydinkh, ...)
I'm not saying it's not possible to get those kind of gains in a day, but I just don't see any stocks that have jumped that much on those days.