Comment # 6 on bug 1130293 from Mindaugas Baranauskas

Seems buggy implementation introduced with 
https://github.com/yast/yast-control-center/commit/c93adf77412d67debe90884ed8dcec3c2f546dd6 

Yes, there I see lines about hicolor as fallback:

    // qt5ct doesn't set a default theme
    if ( QIcon::themeName().isEmpty() )
    {
        QIcon::setThemeName( "hicolor" );
    }

(https://github.com/yast/yast-control-center/commit/c93adf77412d67debe90884ed8dcec3c2f546dd6#diff-1600f20d47e25cf1adc481bd42972e9eR279)