I found the bug in my database code. It was very stupid, of course. But hopefully you will be able to understand my logic flaw. Ok, the endgame is Bishop + Knight versus King. You are on the strong side, and you know you have a mate in 1 move. So I was generating every Bishop move from the position, then testing to see if the enemy King was checkmated. I was also generating every Knight move from the position to see if the enemy King was checkmated.

There, now do you see my logic flaw?

It is subtle. And it is NOT related to the Knight not being able to force checkmate. There are certainly mate-in-1 positions where the Knight seals the win due to an opponent's misplay.

I WAS NOT GENERATING KING MOVES LOOKING FOR MATES IN 1!

It never occured to me that the King could move in such a way to reveal the Bishop and exhaust a flight square for the enemy King, so my mate in 1 list was incomplete. This effects everything else in the database.

Now that it has been indentified, I will recompute the database, then regrade everybody's longest win.

--Ed