On a new installation starting the fonts kcm writes a (wrong) config right away because of the preview image provider. It shouldn't write a config unless something was changed. It also most certainly should revert properly to the original state (= no config). #2 0x00007f70184221b1 in KXftConfig::apply (this=0x7ffdc5055930) at ../kcms/fonts/kxftconfig.cpp:302 #3 0x00007f701840fea6 in PreviewImageProvider::requestImage (this=0x3c258c0, id="0_1.png", size=0x7ffdc5055b58, requestedSize=...) at ../kcms/fonts/previewimageprovider.cpp:111