DPMS keeps getting disabled in XFree 4

[mark@foresthaven.com]

Greetings:

I just upgraded to woody and XFree 4.0 and I have one nagging little
problem. I enabled DPMS for my monitor but it keeps getting turned
off.

For example, I enter the following:

xset dpms 300 600 900
xset +dpms
xset q

...

DPMS (Energy Star):
  Standby: 300    Suspend: 600    Off: 900
  DPMS is Enabled
  Monitor is On

Several minutes later, though I do 'xset q' and get

DPMS (Energy Star):
  Standby: 7200    Suspend: 7200    Off: 14400
  DPMS is Disabled

If T try 'xset dpms force suspend' the monitor goes immediately into
standby mode so I know that the capability is there. Does anyone know
why it keeps getting turned off?

-- Mark