Pythagoras: The algorithm used by the system previously to compute BKR had a bug -- if the players' ratings were less than 400 points apart, then the winner's BKR adjustment was always +8 and the loser's was -8 regardless of which player won. The adjustments should be smaller if the higher-rated player wins, and larger if the lower-rated player wins.

If the ratings difference was larger than 400 points, the system formerly assigned negligible adjustments if the higher rated player won, and relatively large adjustments if the lower rated player won (I'm not sure this has changed!).

Now, the ratings adjustment is always larger if the lower-rated player wins than if the higher-rated player wins.

Formerly, if a high-rated player was careful to play only opponents whose ratings were within 400 points of his own, he was pretty much guaranteed that his rating would continue to rise as long as he won more than half his games. Now, it is very difficult to even maintain a high rating.