http://bugs.winehq.org/show_bug.cgi?id=17670
--- Comment #1 from el elton@schiert.net 2009-03-13 12:39:02 --- A workaround is to create a listen server (with the same map than the server you want to join is running) an then joining the other server.
See here: http://www.svencoop.com/forums/showthread.php?t=35854