Comment # 2 on bug 104808 from Michel Dänzer

This is a gnome-shell/mutter/clutter bug, please report it there.

You can work around it by putting this in ~/.drirc:

<driconf>
    <device screen="0" driver="radeonsi">
        <application name="gnome-shell">
            <option name="allow_rgb10_configs" value="false" />
        </application>
    </device>
</driconf>