I have a Xubuntu 12.04 workstation running vino-server 3.4.2 (for VNC access).
In Power Manager (xfce4-power-manager), the physical monitor is set to sleep after 1 minute of inactivity.
This works well after reboot. However, after I first connect to the machine using VNC, and then disconnect again, the display will always remain on.
(Client used: TightVNC portable on Windows, built Oct 29 2009)
Looks like VNC somehow inhibits the xfce4 power manager.
As a successful workaround, I have created a task that will periodically restart the power manager.
(Using gnome-schedule, create a task that runs every hour. Configure it as "X application (suppress output)")
Better solutions would be welcome. And, how can we find out if it's a problem in TightVNC, vino-server, or in xfce4-power-manager?