title: Root view controller's view disappears when pushing another view controller
body: <p>I am trying to push a <code>UIViewController</code> on my <code>UINavigationController</code>'s root view controller. I am doing this with a custom transition to make it look like a modal presentation.</p>
  
  <pre><code>CATransition* trans = [CATransition animation];
  trans.type = kCATransitionMoveIn;
  trans.subtype = kCATransitionFromTop;
  trans.duration = 0.4f;
  trans.timingFunction = [CAMediaTimingFunction functionWithName:kCAMediaTimingFunctionEaseInEaseOut];
  [self.navigationController.view.layer addAnimation:trans forKey:nil];
  [self.navigationController pushViewController:vc animated:NO];
  </code></pre>
  
  <p>My problem is, that the <code>self</code> view controller's view seems to disappear when I push, so the background behind the modal-presentation becomes black while the transition runs.</p>
  
  <p>This image illustrates the problem:
  <img src="https://i.stack.imgur.com/3dlXX.png" alt="enter image description here"></p>
  
  <p>When the transtition is done the magenta view is visible as expected, but while the transition occurs the green background disappears.</p>