RespondsToSelector returning a false-negative?

I'm currently using -respondsToSelector: like so:

i开发者_运维知识库f (![moviePlayer respondsToSelector:@selector(currentPlaybackTime)]) {
    NSLog(@"Cannot get current playbackTime on %@", moviePlayer);
    return;
}

where moviePlayer is an instantiated MPMoviePlayerController object. I do a lot of other similar selector checks, so I know that pretty much everything else is working fine, but for some reason, this respondsToSelector check returns false, even though if I do something like time = [moviePlayer currentPlaybackTime], it works fine. This is on 4.0+ iOS, so there's no reason for it to return false.

Any reasons why this would happen?

---

According to the iOS class reference, currentPlaybackTime is a property of MPMusicPlayerController, not MPMoviePlayerController.

MPMusicPlayerController: http://developer.apple.com/library/ios/#documentation/MediaPlayer/Reference/MPMusicPlayerController_ClassReference/Reference/Reference.html

MPMoviePlayerController: http://developer.apple.com/library/ios/#documentation/MediaPlayer/Reference/MPMoviePlayerController_Class/MPMoviePlayerController/MPMoviePlayerController.html

It may be a private property of MPMoviePlayerController that does not have an accessor.

EDIT (see comments)

Determine OS version:

float iPhoneOSVersion = [[[UIDevice currentDevice] systemVersion] floatValue];

if ( iPhoneOSVersion < 3.2 )
{

}
else
{

}