While trying to connect to Atze's server (with rejoin enabled) I ran into this message:
[2013-06-07 01:31:48] *ERROR* In [network_interface.cpp::DisplayErrorMessage Line: 143] sErr [client_interface.cpp::updateLobby Unexpected network message: 15]
It was also displayed on screen. The connection to the server was reset and I ended up on the server list again.
A second attempt to connect succeeded, so I'm not sure how to reproduce this, also because I do not know what this code (15) stands for.
Possibly related, I keep having trouble connecting to my in-progress game on localhost occasionally. This seem to be influenced by whether or not the this game is listed on the masterserver and how fast I try to connect. Trying to connect early when the game has just started usually results in a timeout of the client while connecting to the server lobby.