pgt: The link you provide doesn't show the rating change after this match. You should receive a message (under 'Events') that shows that your rating went up and his went down. If not, it seems to be a bug.
pedestrian: > I won this match. How come I lost rating points? It was a 7 game match, which I won 4 games to 3 > > Game ID: 4914333 > ennukene00 is the winner. > > ennukene00: old BKR = 2256, new BKR = 2264 (+8) > pgt: old BKR = 2245, new BKR = 2237 (-8) > > Game type: Hyper Backgammon