Comment 10 for bug 1791367

From the upstream report:

"A possible explanation would be that gnome-settings-daemon is not handling one of the keys that it should be handling. And gnome-settings-daemon also disables the kernels handling of the RFKill keys at the same time.
What you could do:

Check which key is emitted using "xev"
Check the low level key that is fired using "evemu-record" (you'll need to try different input devices)

To be honest, the most likely explanation is that the following xkeyboard-config bugfix has not been merged into ubuntu yet: https://bugs.freedesktop.org/show_bug.cgi?id=100970, patch https://patchwork.freedesktop.org/patch/155965/ which should be in 2.24."

And:

"Just to make this clear. The above means that this is likely a downstream bug in Ubuntu which needs to upgrade (or patch) xkeyboard-config.
i.e. if "XF86RFKill" is not mapped, then xkeyboard-config is outdated and the symptoms you describe fit perfectly."

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The "xev" output that I get is:

KeyPress event, serial 38, synthetic NO, window 0x3800001,
    root 0x1a8, subw 0x0, time 1318232, (131,-31), root:(1962,997),
    state 0x0, keycode 255 (keysym 0x0, NoSymbol), same_screen YES,
    XLookupString gives 0 bytes:
    XmbLookupString gives 0 bytes:
    XFilterEvent returns: False

KeyRelease event, serial 38, synthetic NO, window 0x3800001,
    root 0x1a8, subw 0x0, time 1318232, (131,-31), root:(1962,997),
    state 0x0, keycode 255 (keysym 0x0, NoSymbol), same_screen YES,
    XLookupString gives 0 bytes:
    XFilterEvent returns: False