Re: DPMS over DP->DVI adapter not working
We haven't been able to observe the DPMS failure exactly as you've described it. However, we are investigating other reports of DPMS state failing to stay set, and have been able to confirm these reports. Preliminary findings from the investigation seem to suggest that gnome-power-manager is making DPMS change state after we set it in the driver. There appears to be something of a race condition here, and the problem doesn't reproduce on every configuration. It also isn't specific to any particular type of port, as far as we can tell, so I'm not convinced that your problem is related...
If you could try running a bare X server and/or killing gnome-power-manager (if you're even running it in the first place) to see if the problem goes away, it might give us a clue that your problem (which we haven't reproduced) is or isn't related to the other one which we're investigating (and have reproduced).