A logs back in. In the config message, the number of clients connected is -1, but it should be 0 instead.
B logs back in. B receives a number of clients connected in the config message of 0, but it should be 1 instead. A receives a UD message with unknown uid, and then the NU containing B's uid.
It seems to be a proxy issue.
Scenario: take 2 players, A and B.