title: NSPageController bad transition
body: <p>I have a problem with page controller transition, it looks like this</p>
  
  <p><a href="https://i.stack.imgur.com/iEaOJ.gif" rel="nofollow noreferrer"><img src="https://i.stack.imgur.com/iEaOJ.gif" alt="bad transition"></a></p>
  
  <p>Here is the code of my page controller</p>
  
  <pre><code>class PageController: NSPageController, NSPageControllerDelegate {
  
      override func viewDidLoad() {
          super.viewDidLoad()
  
          delegate = self
          arrangedObjects = ["FirstViewController", "SecondViewController"]
      }
  
      func pageController(_ pageController: NSPageController, identifierFor object: Any) -&gt; String {
          return object as! String
      }
  
      @IBAction func forward(_ sender: Any) {
          self.navigateForward(self)
      }
  
      @IBAction func back(_ sender: Any) {
          navigateBack(self)
      }
  
      func pageController(_ pageController: NSPageController, viewControllerForIdentifier identifier: String) -&gt; NSViewController {
          return storyboard!.instantiateController(withIdentifier: identifier) as! NSViewController
      }
  
      func pageControllerDidEndLiveTransition(_ pageController: NSPageController) {
          pageController.completeTransition()
      }
  }
  </code></pre>
  
  <p>Why does it look like this and what can I do to achieve normal transition?</p>