As stated on the upstream bug report, this is a 'normal' behaviour. 'Revert' will use the system default, and since we don't ship any in xubuntu (because it depends on the screen resolution), the key disappears (but it'll re-appear when you start xfce4-settings again).
As stated on the upstream bug report, this is a 'normal' behaviour. 'Revert' will use the system default, and since we don't ship any in xubuntu (because it depends on the screen resolution), the key disappears (but it'll re-appear when you start xfce4-settings again).