The title pretty much says it all. I opened a new purchase from Amazon and it worked fine. I changed the orientation of the PB to portrait and the book didn't change. I checked to be sure the orientation wasn't locked. It wasn't. The problem now exists for all the books in the Kindle app. Everything else is fine. I've rebooted and that hasn't helped. The problem does not occur in other readers. Does anyone have an idea what's going on? Thanks.