title: object in addObserver is different
body: <p>I'm have the following code:</p>
  
  <pre><code>[[NSNotificationCenter defaultCenter] addObserver:self selector:@selector(moviePlayerWillEnterFullscreen:)
                                               name:MPMoviePlayerWillEnterFullscreenNotification
                                             object:nil];
  </code></pre>
  
  <p>And the method uses a property of self:</p>
  
  <pre><code>- (void)moviePlayerWillEnterFullscreen:(NSNotification *)notification
  {
      NSLog(@"%@", self.videoItem._id);
  }
  </code></pre>
  
  <p>Sometimes (not always) the self object inside the handler is a different object (and an uninitialized one which causes a crash)</p>
  
  <p>I can't seem to figure out what am I doing wrong, and how to avoid this case. 
  Is the <code>"self"</code> object gets copied?</p>