title: Add UIViewController from another Storyboard
body: <p>To get more structure in my project I started to use multiple storyboards.</p>
  
  <p>Now I want to push a ViewController from another Storyboard. This works as aspected with no warnings. Unless I open the ViewController for a second time.</p>
  
  <p>The push produces this error message: "nested push animation can result in corrupted navigation bar" and on pop it results in a crash with this message:
  "Finishing up a navigation transition in an unexpected state. Navigation Bar subview tree might get corrupted."</p>
  
  <p>I push the ViewController with this code:
  [self.navigationController pushViewController:controller animated:YES]; </p>
  
  <p>I assume there is something wrong with the NavigationController.</p>