after using dpkg --purge and apt-getting snx again, /etc/xbindkeysrc.snx returned. It contains:

"wmctrl -r :ACTIVE: -b toggle,fullscreen"
F6
"wmctrl -r :ACTIVE: -b toggle,fullscreen"
F10

It strikes me as odd that both entries seem to toggle fullscreen, which button is F6?

And I tried camerabutton and ctl-return both in the original terminal and in the NX terminal, to no effect. BTW: Switching to full screen works when I replace the F10 by Control + KP_Enter

AFAIK I have a normal keyboard and again afaik there are noprograms running that change the keyboard.
snx is listed as version 0.1.3-3

I really appreciate the trouble you take in answering me.