If you are in an app in landscape mode and hit the home screen button you can periodically get this screen. Why would you want it? The auto rotation feature itself is only supported in apps that support portrait and landscape. The sense UI home screen doesn't really support it. It just is a flaw in the rotation from the app that does support it. This hasn't done it to me since I have had 2.1 installed though..must have have been a 1.5 bug.