Guys..... read my lips... IT HAS BEEN SOLVED! This has already been reported......Blade and Ed have been testing the new firmware for some time now and have reported that this issue has been fixed.
It will be incorporated in the next firmware release and you will get no more GPS/Atti problems (or gimbal twitch which is associated with the same thing).
It has been caused by an overly sensitive setting on the compass data which as a precaution causes the craft to switch to Atti when it senses abnormalities/conflicts with GPS v Compass.