Comment # 10 on bug 1105792 from Fabian Vogt

(In reply to Ludwig Nussel from comment #8)
> That is rather old, maybe fixed on 15.1? In any case we need to pull in the
> theme at least for yast2-firstboot.

I can still reproduce the issue on Tumbleweed at least. It seems to be a race
condition involving the YaST QSS stylesheet, combined with running on the
secondary monitor and using the KDE breeze theme. So far I haven't been lucky
with debugging. (boo#955381)

I didn't try the SLE theme, but I assume it hits the same underlying issue.