Comment # 15 on bug 1105792 from Stasiek Michalski

(In reply to Fabian Vogt from comment #14)
> It looks like as part of the theme changes the default theme YaST picks if
> run outside of firstboot/installation ("style.qss") is not a full style
> anymore and so does not trigger the crash.
> 
> So installing yast2-qt-branding-openSUSE shouldn't be an issue anymore
> AFAICT.
> 
> If style.qss changes in the future, this will need to be reevaluated.

Just as a sidenote here, this was done on purpose, plugins for styling in Qt
are clever enough to load the rest of the theme as they would system wide, so
only elements used as branding (mainly sidebar) are styled differently than the
rest of the system.