I'll add to the anomaly. As of the close, freerealtime.com shows 41 trades with total volume of 21,400 shares. Since the last trade was 100 shares, I don't see how freerealtime could have shown 40 trades and volume of 20,500 at 3:05 ET when you posted your message. The last trade needed to be 900 shares to add up to 21,400.
PC Quote shows 41 trades and volume of 21,400 shares. Signal shows 41 trades and volume of 21,400 shares. BWAC is correct that some services add pre-open trades and others don't. This is the most likely reason for the discrepancy that you noted although I thought quote.com added pre-open trades.
Another possibility is that you might be receiving delayed quotes even though you think they are real time. If you meet me on IRC or AOL one day, we can compare a few symbols in real time to see if your quotes are working properly. Send me a PM if you want to try it.