this has nothing to do with sensors or switches right? this is just what would happen with any camera or camcorder I believe.

the difference is that the image is not like looking in a mirror, but is inverted. so when holding at 90 ° you see an upside down image rather than the same way up.

the only switch I know of is if you rotate the camera to point to the back of the n800 then you notice it cut out and back in again as it inverts the image to still show as the right way up on the screen.