iOS8 AVPlayerItem を 変更時 アプリが落ちる

Terminating app due to uncaught exception 'NSInternalInconsistencyException', reason: 'An instance 0x17001f8c0 of class AVPlayerItem was deallocated while key value observers were still registered with it. Current observation info: (
Context: 0x0, Property: 0x170055ae0>

AVPlayerItem* item = [[AVPlayerItem alloc] initWithURL:url];
[item addObserver:self forKeyPath:@"status" options:0 context:nil];

// これがないと落ちる
[item removeObserver:self forKeyPath:@"status"];

item = nil;

item を 解放する前に、Observer を削除しなけらばクラッシュするようになった。