Ok so overall: Qt5/plasma5 based app - subpixel Qt4/KDE4 based app - no subpixel Gtk2 app - no subpixel You can also try some gtk3 app (gedit/etc). Overall no clue why the subpixel is not used on the others, because the app itself should ask fonconfig for the right glyphs and the app itself usually decided based on the fonconfig settings, that you set system-wide in yast2 fonts.