Not surprising! From the looks of it I'd say it isn't even running jj2. It appears to be some sort of semi-working dedicated server software. The server responds to client TCP requests, but they haven't bothered to implement the UDP protocol yet. People would receive the "server stopped" dialog because the server appears to intentionally disconnect the player shortly after joining by sending a couple of disconnect packets. It also sends some weird and inaccurate data to the list server. This server is harmless.