I found out that with second screen attached, but without external USB (cable bound) keyboard everything works as desired. I will try to find out, if this is a problem of this specific keyboard
edit: I cannot reproduce this working scenario any more, so I apologize for this misinformation. Maybe it was a fata monitoriana...
edit: I cannot reproduce this working scenario any more, so I apologize for this misinformation. Maybe it was a fata monitoriana...