I do have all that set…
There is some odd hidden internal state that switches it.
Just saw full HD 3D, just gorgeous, huge improvement. Did try bypassing receiver and changing TV HDMI port (while hot) to get it going initially. Then switched back thru receiver and still running until I played a HSBS file then it was stuck again in the HSBS mode playing MVC file. Reboot and can play full HD 3D again until I play HSBS file then broken.
Unfortunately the RPi1B is not capable of running this high a bit rate (~40Mb/s MVC) 
- it stops to buffer up quite often and loses A/V sync. Rubbish really and locks up and freezes quite often as well. It is not the hardware as ran Raspbmc OC faultlessly for years and I am back to regular clock and still have lots of freezes when playing around trying to get 3D operating - often at keyboard entry. Been a total waste of a couple of days time… thanks anyway. Need RPi2 after all - or recode MVC but not yet supported in ffmpeg.