As this does not happen with GNOME and has not been reported for
Fedora 12 or older, does anyone know what the problem could be?
With a fresh install of F13 KDE x86_64 and default KDE settings, Audacious
starts with dark-grey fonts, which are hardly readable:
System Settings > Appearance > Fonts
Here I don't need to change anything. It is sufficient to click something
and revert it again, then click the "Apply" button which gets enabled by
that action. Immediately afterwards, the fonts/dialogs in a restarted
Audacious become readable until next reboot.