lockdown settings not locking ability to lock screen

Binary package hint: gnome-screensaver

I have the below settings in a lab, to lock the environment down, to prevent screen locking and user switching and other bad habits in this context. It is all mandatory gnome settings. I set it with

gconftool-2 --direct --config-source xml:readwrite:/etc/gconf/gconf.xml.mandatory --type blah ....

/desktop/gnome/lockdown/disable_lockscreen_and_logout true
/desktop/gnome/lockdown/disable_lock_screen true
/desktop/gnome/lockdown/disable_user_switching true
/apps/gnome-screensaver/user_switch_enabled false
/apps/gnome-power-manager/can_hibernate false
/apps/gnome-power-manager/can_suspend false
/apps/gnome-screensaver/lock_enabled false

It works fine up to a point. In the logout dialogue there is only the logout option. In the system menu there is no lock screen. In the screensaver preferences these things are greyed out. However, the ctl-alt-l default key is still able to lock the screen (or running gnome-screensaver -l).

I'm assuming gnome lockdown settings (disable_lock_screen) should affect gnome-screensaver too?

I think one should have both the option to remove it from menus (as it does now) and a further option to actually disallow users from running it.