Mine did this a couple of times last night and I thought I was going crazy. But after I closed the flip shut and reopened it again, it was fine. You have to make sure that you don't, in any way, accidentally rotate the screen the wrong direction (even slightly) before spinning it to the direction you want it.
It seems that it must be something wrong with my phone then. It takes more than a half turn to switch it to landscape when twisting the normal use way (even though it still flips the screen to the self portrait way) but when I flip it to the actualy self-portrait way (clockwise) I dont hardly have to turn it at all.
That upside down imaging, is a defect. I had two 970s and both did that at some point. Your image should always be right side up, no matter which way the display is turned. Something isn't computing properly within your phone.
If you are within the 15 day trial, you can swap the phone for another new one. If you have exceeded your 15 days, they'll still swap it out but you'll get a refurbished phone instead.