I know this problem comes up from time to time, but this time it is quite - strange. playing videos (fullscreen) in vlc did not turn off screensaver/power management.
vlc-1.1.12 (also tested 1.2.0_pre1), kde-4.7.3 - and (guess) vlc does not inhibit power management (though the option is turned on).
So I created a new power profile "Video", where I disabled all checkboxes, so no dim or switch off monitor should appear. Changing to this newly created profile, works great - until I start vlc. vlc seems to change some settings, so that the monitor turns off (although it is disabled in the powerdevil settings!). And this behaviour stays after closing vlc. Only solution: Change profile to "performance" and again back to Video.
I have to disable the "inhibit power management ..." and "disable screensaver" options in vlc in order to not get interrupted by the monitor turning off.

I am not entirely sure anymore, but I think vlc changed this behaviour after reinstalling. (vlc was installed together with kde-4.7.2, Update to 4.7.3 did not change vlc's behaviour, reinstalling vlc with kde-4.7.3 turned vlc unusable). Could it be, that vlc takes some info about pwm at compile time? Or is it just my bad memory :/

I am asking this here at kde forums, as in the past, vlc immediately blamed KDE for not properly implementing the feature...

Thx
Franz

VLC runs a series of commands intended to disable screensavers and the like when it commences video playback. These could easily be related to this issue (especially if one of them happens to be invoking GNOME commands....).

Unfortunately, i'm not sure which commands it runs (but I know it did run some scripts, as on my older openSUSE 11.3 install, a script would generate a error relating to kde-config, which comes from KDE3 which I didn't have installed). VLC itself doesn't ship with these scripts.

Thx for your answer. So you say, vlc just "shoots around, hoping to hit as many marks as possible"? I am running just kde, gnome-dependencies are only installed where needed (e.G. with glib, upower, policy-kit). I run Gentoo, gnome-USE-Flag is disabled globally, as is gtk.
So the solution is to find out what commands vlc is actually calling and fix them? I will have a look if I can find the calls in vlc-sources :/

More answers/solutions are still welcome

From what I have seen, the commands are probably xdg-* commands.