Unavailable keys in 4.3.90.1

[Mtc]

> Xfce doesn't do anything special with key syms and rely on the 
> configuration of the system for that.
> 
> Xorg 6.8.x and later seem to have a bug and don't set that key as a 
> modifier.
> 
> Cut'n paste the following lines to $HOME/.Xmodmap and restarty your session:
> 
> clear mod4
> add mod4 = Super_L

That helped, thanks a lot.
However, I don't understand one thing, if it's only an X problem, why 
wasn't this change needed to have the mod4 key available when editing 
shortcuts in keyboard preferences?

-- 
Best regards,
Mtc