Server 4510 has been released.
http://www.3cx.com/forums/3cx-phone-system-v5-1---new-build-4510-18th-april-5040.html
Of course it's not the exact same version number as the client, and I'm going to try to install that today and see if it works with the latest client build. It does say you must have the latest version of the client installed in order to see extension status, so going with that 4492 should work I guess. We'll see...