1) Install WireShark on the same machine as MC server.
2) Shutdown all apps that you can on your server to minimize the traffic
3) Start MC12, make sure the Library server is running
4) Start Wireshark and begin capture
Capture->Interface->start on proper interface
5) On MC running on the client machine initiate a search for libraries
6) Stop capture an look for the servers UDP response in the capture log.
http://tinyurl.com/37kkq6On the capture above, look at messages 3001 - 3004. These are the request/response packets for MC. I highlighted the one from the problem server so you can see the data in the data window.
It has the right name and port - pinot and 85, but you can see the IP address in the response is 0.0.0.0.
Try the same experiment and post the contents of the server's response packet. It will be a UDP packet sourced on port 5556 like mine.
Cheers,
Derek