Interesting. The GW1000 and 1100 work just fine with the MX web server. I've also created my own server for intercepting Ecowitt data calls (I have to manipulate it a bit before passing it to MX) and the GW1100 works just fine with that too. It looks increasingly like there may be a bug in the GW2000 firmware.
It would be informative to hear if anyone else on the forum is using a GW2000 to pass extra sensor data to MX - and whether they are experiencing the same issue.