Hello Tim,
> instead of downgrading (see mail of Tim Mueller) you also could execute
> xmodmap -e 'clear mod1' -e 'add mod1 = Alt_L'
> on the console.
thanks a lot, that did the trick.
>
> This is not permanently. After X restarting you have to do it again.
Of course, I will try to insert this somehow into my .Xmodmap (have already
forgotten the syntax, but this shouldn't be so difficult).
Thanks again, also to Marcus and Tim Müller,
Bernd