I uninstalled screensavers and keybru, so my DXG has the same hacks as the DX. The "missing keys" problem is still present.
I verified that keycodes reported by waitforkey are correct, and the DXG has the same myts keydefs.ini file as the DX.
*Something* must be different between the DX and DXG. I suppose I need to factory reset and reinstall everything ;-(