This seems to be the intended behaviour. If Apple would want you to react to authorization changes at runtime, there would be a notification that tells you that it changed.
But right now, there is no such notification (as far as I can see). You just call +authorizationStatusForMediaType: and it either returns a definitive status (like denied or authorized), or it returns AVAuthorizationStatusNotDetermined to tell you that you need to request authorization via requestAccessForMediaType:completionHandler:.
Unfortunately, this isn't an authoritative answer; I'm just drawing conclusions and guessing here. You might want to ask on Apple's developer forum and hope to get an answer from an Apple engineer.
