Opponent resigned right as I checkmated them

I thought this was silly. My opponent resigned the moment I played ..Qxh8# (position shown below), and the "You Won!" screen still said I won by checkmate.

What makes it even funnier is that I didn't even realize it was checkmate until I looked at it again. I thought I was simply getting both of the rooks for free. Mildly amusing moments like this are just another small reason why I keep coming back to the game.

ok

GG

I would be inclined to believe that it has to do with timing. If the person resigned, you shouldn't have been able to move. If you mated, then he shouldn't have been able to resign. But if both took place at the same time perhaps it put the program in a quandary? Nice win.