[palosanto]

I know this is a very old post but maybe is good to share that I was facing a similar problem in Windows with my new dell Lattittude 5290 2-in-1.  The system orientation lock was always on and locked.
I discovered that this is the case if the keyboard is attached.  When detached, the lock can be switched off and the tablet auto-rotates which is ideal if you use MSP in portrait mode and there's no need to change the orientation in windows every time you use it.