Comment 1 for bug 33523

i'm pretty sure this is a duplicate of #22018, can you check the dpms settings of gnome-screensaver with gconf-editor ? gconf doesnt delete user settings on upgrades, so if someone had the broken package installed early in the release cycle and changed a setting, the complete set of broken settings persists.
to get the shipped defaults, you can try to flush the user settings with:
gconftool-2 --recursive-unset /apps/gnome-screensaver