[cctalk] Editing files in VMS over a telnet connection

I feel like I have tried everything, although I'm sure I haven't... I have my real MV 3100 up and running with a serial terminal on the console port. It works great but I don't want to sit by the machine all the time to do stuff. I have DECnet running and am able to connect to it. I have an old raspberry pi running a minimal linux setup with the decnet stuff installed. So I ssh to the pi (named gatewy) and from there I use dnlogin to talk DECnet and connect to the machines. This way I can connect to my PDP-11 machines running RSX11M and M+ and use EDT to edit files in screen mode. When I try the same under VMS, EDT starts, loads the file and enters screen mode but just shows a blank screen with the cursor in the top-left corner. If I go to line mode I can walk through the file and edit using line mode. But as soon as I go back to the screen mode (the change command) I just get the blank screen. I have made sure TERM in each shell is vt100 and I have tried forcing VMS to VT100 but it stays with a vt200_series terminal. I also have a SIMH MV3100 also running VMS 5.3-1 (they both run on that version) and it acts the same way as the hardware MV3100. If I go onto the console connection in SIMH EDT works fine, as on the physical terminal on the real machine. Anyone have any pointers or ideas I can try? - Peter