QAbstractSocket::ShareAddress has no effect for multicast sockets

Take the multicastreceiver in the network examples. Change groupaddress to 239.255.255.250 and port to 1900. Leave rest of code unchanged. Start multicastreceiver twice. The second time the following error message is printed to console: QNativeSocketEngine::joinMulticastGroup() was not called in QAbstractSocket::BoundState
239.255.255.250/1900 is UPnP multicast. When one listener is connected to this socket, no other program can use it. This prevents for instance multicast UPnP messages of an XBMC running on the same machine. This bug does not happen under Windows 7/mingw-4.8.1/Qt-5.1.1.