
You might have noticed that your Halo 3 stats don't look quite right; that's because they're not. Some corrupted data was preventing player information from being uploaded to Bungie.net, causing the discrepancy in game stats. In other words, your game info is being recorded, it just can't get where it needs to go at the moment. A post from Bungie's Luke Smith explains the issue in a bit more detail:
They know what's going on, they're working on it, should be fixed in a jiffy.
OMG My Stats Are Borked! [Bungie.net]