It's actually that it shows the mirror when you're taking the shot "mirrored" and then the actual picture saved is correct. I understand you find this frustrating, but would you think about this:
Wouldn't it feel kind of wierd if the picture on the screen while you are angling the camera, would show you in the way others see you? It would mean if put your finger on your left cheek, on the screen it would be on the right side.
My opinion is that that would feel really wierd, and that it's way better the way they do it now.