there is no error at all, the game main page reloads and you are asked if you want to rejoin or forfeit the game, when you click rejoin you go back to where you were but now you are a single player and obviously forfeit ends the game. i tried a game twice last night with a guy called youngsaint and the first time it was just the 2 of us so he came out as he wanted to play with others. the 2nd game was 3 of us and so he carried on with the other player when i got booted.
i can't think of anything else that happens but its easy to check out yourself, just start a game with 1 other person so the chat box is available and type nt (nice try) without entering it in that 'type message here' box.