It's not a bug. There is a formula for the way XPs are handled after a race that factors in the average amount of points for the people in the race and the order they finished in. I don't know what the formula is, but you are rated higher than anyone else in the race, so even though you you finished well, you didn't gain any points. On the other hand, you didn't lose any points either. I've seen people lose points for winning their race when the league is small and they are better than their competition.