MPMoviePlayerController - AVSystemController_SystemVolumeDidChangeNotification called not right

Question

I have MPMoviePlayerController and i m trying to get notify when user change the volume.

I listen to this event: AVSystemController_SystemVolumeDidChangeNotification by this code:

   [[NSNotificationCenter defaultCenter]
 addObserver:self
    selector:@selector(moviePlayerVolumeChanged:)
        name:@"AVSystemController_SystemVolumeDidChangeNotification"
      object:nil];

And i catch the notification in:

- (void)moviePlayerVolumeChanged:(NSNotification*)notification {
    klogdbg_func
    // GA
    [self trackVideoPlayerGAEvent:@"Change Volume"];
}

The problem is that my player notify me 4 times when the movie start/finish loading, without any volume change by the user.

Why that?

Thanks in advance!