If I win or lose an online game, it shows up in the stats after the game but then when I exit back to the main menu, the stats are lost.

Is this a bug or what?

The stats are held for that play session only.

The stats are held for that play session only.
OK. Would have been nice to be able to keep track of your wins and losses.

In ranked games, you can see your wins and number of games played on the leaderboards.

except ranked games stats = how lucky you've been dodging all the loosers who switch off or disconnect as soon as their behind. or indeed how big a looser who discon's you are.