<EOT>, CHR$(4) is sent by xmodem but only at the end of all text so it shouldn't be doing anything at the time.
Phil has confirmed the problem so I might change the firmware to VGA and do some investigating if time permits today. Spring time so lots to do.
My guess is, there is something that gets cleaned up with a ^C that doesn't get cleaned up with a simple END. I am not sure if there is any way to simulate a ^C from within a program. 'ERROR' seems the closest but not very nice for the end user to see.