title: CATransaction completion being called immediately
body: <p>I'm trying to execute a completion-block after my CAAnimation has finished. However, it seems that animation block is called before my animation completes. The animation still happens correctly though.</p>
  
  <pre><code>[CATransaction begin];
  [self.view.layer addAnimation:self.dropAndBounceAnimation forKey:@"appearance"];
  [CATransaction setCompletionBlock:completionBlock];
  [CATransaction commit];
  </code></pre>
  
  <p>The dropAndBounceAnimation is a CAKeyFrameAnimation on position.y, with a fixed duration.</p>