Single-Stage vs Two-Stage Animation for iPhone Apps?

Question

What are single-state and two-stage animation for rotating an iPhone window?

This is the \"error\" message I get in the Debugger Console (nothing crashes):

Answer 1

I have found the culprit in my case to be the UIImagePickerController (I also do not override any rotation animation):

[self presentModalViewController:imagePicker animated:YES];

Replacing imagePicker with a generic UIViewController doesn't generate any warnings.