to me, I wouldn't be surprised if overlapped I/O on sockets are to blame a +ntdll trace would be helpful
How do I enable that? (likely a noob question)
From your comments I take it's no setup problem on my side, could be a real bug.
Meanwhile I got some more info from the developer, relaying your responses, sorry for the odd communication. ;-)
I used that to create a fully featured bugzilla entry: http://bugs.winehq.org/show_bug.cgi?id=6415
Thanks Jörg