Now I have done some investigation on this and found out the following.
The setting for this is held in the database.
It is in mythconverg database in the settings table.
This table has a structure consisting of 3 columns called 'value' 'data' 'hostname'
There are on my system about 1800 rows in this table which from looking seems to hold 99% of all settings for myth.
The value which is effected by this issue is 'DefaultVideoPlaybackProfile' Now when I search on this I get a value for each of the my media directors with a hostname of 'moon*'
Now when I set the options in mythtv on each media director to use 'VDPAU Slim' this is reflected in the 'data' field for that media directors in the database.
From this I can assume that the frontend is commiting the changes correctly to the database. This is further evidenced by the fact that I can open and close livetv and also reboot the individual media director and it keeps the settings.
Now when I reboot the NerveCentre and check back to the database, even without booting up a single MM it has changed these values in the database back to CPU+
Now what is interesting here is that I have some entries in the database for media directors I have deleted and therefore have an orphaned entry in the mythtv database, now these entries remain untouched and will stay on the setting they were on before reboot.
I can only asume that there must be some script running on NC boot that is amending the settings for this back to default
Any ideas what script might be doing this? There are a lot of scripts!