vlc won't inhibit screensaver as asked in preferences

Even if I check in the preferences that the vlc media player wouldn't be interrupted by the screensaver, when I am looking at a video without moving the mouse or touching the keyboard, the screensaver is activated after 5 min.

It is activated by default in VLC in setting tools > preferences > show settings: all > advanced > inhibit the power management deamon during playback.

My screensaver is controlled by the application System > Preferences > Screensaver. In Screensaver, the computer is regarded as idle after 5 min and the box "activate screensaver when computer is idle" is checked.

I expect the screensaver not to be activated when a video is playing back.

I run Ubuntu 9.10, Karmic Koala, and have Compiz settings as well as Cairo-dock enabled (with open GL).