kcmshell4 fonts - Configure doesn't saves any flags for 'Exclude range' or 'Use sub-pixel rendering' fonts. Reproducible: Always
It works here. Can you please check file "~/.config/fontconfig/fonts.conf" before and after modifications done at the Fonts kcm module?
Recently I deleted ./config/fontconfig/fonts-conf file and checked again. Now seems it saves flags but file fonts-conf still didn't appeared.