title: Flip transition of UINavigationController
body: <p>I have two different UINavigationControllers. Both are customized to present their own cool Navigationbar and have lots of ViewControllers with content. </p>
  
  <p>I figured, it would be good to override the UINavigationController. </p>
  
  <p>Now when I want to flip between the two UINavigationControllers the Navigationbar of the previous and next UINavigationController jump up and down.</p>
  
  <p><img src="https://i.stack.imgur.com/gTO5e.png" alt="When flipping additional space is added to the UINavigationBar"></p>
  
  <p>After the transition is completed, the move back to their original y Pos. 
  Any Ideas?</p>
  
  <pre><code>ViewController2 *VC = [self.storyboard instantiateViewControllerWithIdentifier:@"NavigationController2"];
  [VC setModalTransitionStyle:UIModalTransitionStyleFlipHorizontal];
  id rootViewController = [[[[[UIApplication sharedApplication] keyWindow] subviews] objectAtIndex:0] nextResponder];
  [rootViewController presentViewController:VC animated:YES completion:^{
      //[self removeFromParentViewController];
  }];
  </code></pre>