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According to Microsoft's documentation sockets created using socket() have the
overlapped attribute, but sockets created with WSASocket() do not unless you 
pass the WSA_FLAG_OVERLAPPED flag. The documentation for WSADuplicateSocket()
says
 If the source process uses the socket function to create the socket, the 
 destination process must pass the WSA_FLAG_OVERLAPPED flag to its WSASocket 
 function call.
This means that dup_socket() in socketmodule.c should use
 return WSASocket(FROM_PROTOCOL_INFO, FROM_PROTOCOL_INFO,
 FROM_PROTOCOL_INFO, &info, 0, WSA_FLAG_OVERLAPPED);
instead of
 return WSASocket(FROM_PROTOCOL_INFO, FROM_PROTOCOL_INFO,
 FROM_PROTOCOL_INFO, &info, 0, 0);
(On Windows, the new multiprocessing.connection.wait() function depends on
the overlapped attribute, although it is primarily intended for use with pipe 
connections not sockets.)
Patch attached.