Some time ago, I posted that DPMS screen screen-shutoff mysteriously
stopped working, and later just as mysteriously started working again.
I've finally figured out the culprit by accident...  dosbox.  There are
various MS-DOS game archives on the internet with over 4 decades of very
entertaining games.  I use "dosbox" to run old stuff.

  If I'm in the middle of a game "level" and want to continue it later,
I can window-ize dosbox, {ALT}{PAUSE} to toggle execution off, and then
minimize the window.  Later on, I can bring up the window, {ALT}{PAUSE}
to toggle execution on, and maximize to fullscreen "text mode".

  The only problem is that DPMS screen powersaving does not work while
dosbox is running, or even suspended with {ALT}{PAUSE}.  This is not
specific to any one game.  Even a dosbox window at a command prompt
disables DPMS screen-off.  I've compared the output of "xset -q" with
and without dosbox running, and there's no difference.

  Has anyone else noticed this, or is it something weird with my config?

--
There are 2 types of people in this world
1) Those who can extrapolate from incomplete data