xbmc cannot set resolution/refresh properly with nvidia cards in 12.04

Recently, I upgraded my XBMC Eden / 11.10 Ubuntu box to 12.04LTS, which pulls in a newer version of xorg and the nvidia proprietary driver. My HTPC setup is a single Samsung HDTV connected using HDMI. XBMC is started straight from lightdn as a Xsession.

After I experienced some judder in playback after the upgrade I discovered that in Settings/System/Video output some (fullscreen) options are 'locked'. To be precise; Resolution is locked to 1920x1080 (which is correct, but before I was able to change other resolutions) and Refresh Rate is locked to 0.00.

My xorg.conf does have some custom modelines (25,50 and 60Hz) for my HDTV, which have been working just fine (up to 11.10). Disabling those didn't solve this problem.

Xorg does not log any errors. In xbmc.log I found some errors:

# cat xbmc.log | grep ERR
10:05:26 T:139932101392256 ERROR: CXRandR::Query - unable to open xrandr xml
10:05:26 T:139932101392256 ERROR: GLX: Same window as before, refreshing context
10:05:29 T:139932101392256 ERROR: CheckDisplayEvents - no display event after 3 seconds

I noticed there is an issue involving DynamicTwinView (i.e. ticket 12799). When "DynamicTwinView" is enabled in xorg.conf, the output of xrandr seems complete bogus (showing refreshes like 51,52,53,54,55,56,etc) for my main resolution 1920x1080. Using this setup video playback is chunky and XBMC shows a fairly random refresh rate from that given range when I press O. Disabling "DynamicTwinView" results in sane xrandr output, i.e. showing the actual modes I configured for the panel (25,50,60Hz) at 1920x1080. Video playback is then ok, but the refresh is alway at 60 when I press O during playback. Also, the option to change refresh rate to match video content has stopped working in both cases.

For reference:
Ubuntu 12.04 LTS
xbmc 2:11.0~git20120423.cd20772-1
nvidia-current 295.40-0ubuntu1
linux-image-3.2.0-24-generic 3.2.0-24.37
xorg 1:7.6+12ubuntu1

For reference, this is a shameless copy of the bug report on xbmc trac, but I think it's usefull here too as it affects all using xbmc+nvidia drivers with default 12.04 LTS packages.
Possible workaround upstream is using the new 302.xx nvidia beta binaries that have a proper RandR implementation, however that also requires Xorg 1.12 and 3.4 kernel which sounds more like Quental than Precise.

More info here: http://trac.xbmc.org/ticket/12993