I know it's trivial, but this has never happened to me before. In all the years I've had minesweeper on my computer, I've never had it come down to a 50/50 guess where I didn't pick right. I always assumed that if there was no logical way to figure it out, it defaulted to your guess.
So I figure I've either had the best luck in the world since Windows 3.1, or I had terrible luck by missing out on a person best time.
If I'm just missing a logical way to eliminate one of the choices, I'd like to know what it is.