This is a known issue on Linux. The reason not everyone sees it (and it disproportionally affects Arch users) is because it only breaks with certain font settings.
You can try playing with your anti-alias settings to work around this while you're waiting for the fix: changing the hinting strength to a different setting from the one you're using now should give you your anti-aliasing back (check KDE's or Gnome's advanced font settings to change this).