Hi. I'm using ubuntu 12.10 and even in this distro, after so many year I have the same bug: gnome-shell start screen saving while reproducing videos with vlc in a connected monitor.
the problem is only with vc while totem is able to suspend the energy saving.
funny thing is that in system settings the configuration is that screensaving kikcs in after 1 hour but with vlc, no matter how, after 10 minutes the screen goes blank