I unexpectedly wound up with about half dozen of my portrait photos rotating to landscape in the camera roll of my Titan. Some as far back as January of this year. Has anyone seen this before? I wound up correcting them by connecting my phone to my PC, launching Zune and then downloading the "correct" orientation photo from my Skydrive. This seemed to immediatly update the photo on the phone. I did have one landscape photo that rotated itself 180 degrees and was upside down. The only recent different things I've done recently is to take a couple of panorama photos, and took a video with the front facing camera (and that front-facing video also rotated itself in the camera roll).
I've had several landscape photos turn out upside-down as well. I haven't done a scientific study, but they were pictures of my cats on the floor, and the phone was pitched significantly, so perhaps it's related to that.