I haven't checked the players in your game stats yet, so take this with a grain of salt:
I'm pretty sure that your stats go up when you beat a team of people who have a higher rank than you, and your stats CAN go down if you beat a team of people who are ranked (much?) lower than you.
I noticed several games vs several top 10-20 people, with a couple of wins, made my stats jump up by 100 or so positions. Granted it didn't change my win%, but it sure repositioned me in the ranking tables quite drasticaly.
IMO, the in-game display should show your custom game rank instead of your win %. It would lead to more balanced games, and fewer people will try to use disconnect errors to get a win: They should do away with displaying the win % anywhere and just go by rank relative to other players.