Odds of Royal Flush?

[paul1]

1/1960=0.00051.

Again, I ran some hands on Poker Probe. I matched AK-spades against AK-hearts, ran them 2,500,000 times. Between the two of them, they came up with about 3100 royal flushes out of 5 million hands.

That's 1/1600.

So, what am I doing wrong?