I have tried to post but here it goes again. I have been in dules with people and as I am about to hit with the killing blow the game freezes. I then send them a message to tell them what a Piece they are and it says that their gamertag does not exist.
I've had the same thing happen a bunch of times. When this happens the person (you) lags out, and the other person gets the win. You don't actually disconnect, you're just teleported into a frozen "Single Player Custom Game". If you press Start, you'll have
an option to "Restart Duel", which will freeze your Xbox.
The only way I've found to avoid this is to ALWAYS HOST. I've had no problem when I create the lobby. Hopefully not everyone reads this, because everyone will sit by themselves in lobbies for hours =P