I’m pretty sure this is just a bug in iOS 8.0. It’s reproducible with the simplest of POC apps that does nothing more than attempt to present a UIImagePickerController like you’re doing above. Furthermore, there’s no alternative pattern to displaying the image picker/camera, to my knowledge. You can even download Apple’s Using UIImagePickerController sample app, run it, and it will generate the same error out of the box.
That said, the functionality still works for me. Other than the warning/error, do you have issues with the functioning of your app?