Thank you Nick and Charles for your suggestions. Charles I favor your suggestion of slight deflection in blade and arbor. I do see a slightly wider groove at the head of the groove on the side that isn't square.
Nick, I have been careful to keep the pressure straight forward. Also, I get the same behavior with all three of my blade types. I wiil look for a lifting on one side. On my recent project I was crosscutting a half inch thick piece of maple which is 4 inches wide. The maximum deviation from square is about 1/32 over the 4 inches.