Hello Bernhard, I looked into my normal users env and through this found this line in my .xsessionrc export QT_STYLE_OVERRIDE=gtk2 I think I put it there so that qt apps will pick up gtk theming (which makes running both qt and gtk apps a lot prettier). Commenting out that line, SuperCollider works fine. Interestingly, it even seems to use the gtk theme. So not sure how you see it, but I think that this is more a case of borking one's own system and not a bug.
Thank you for your help. Best regards, Knut
