title: Navigation bar title bug with interactivePopGestureRecognizer
body: <p>I am having a weird problem with <code>UINavigationBar</code>'s title in an app when <code>interactivePopGestureRecognizer</code> comes into play. I have made a <strong><a href="https://github.com/aksh1t/iOSNavigationBug">demo app</a></strong> to showcase this bug.</p>
  
  <h3>Setup:</h3>
  
  <ul>
  <li>The rootViewController is a <code>UINavigationController</code>.</li>
  <li><code>FirstViewController</code> has the navigation bar hidden, and <code>interactivePopGestureRecognizer.enabled = NO;</code></li>
  <li><code>Second</code> and <code>ThirdViewController</code>s have the navigation bar visible and the popgesture enabled.</li>
  </ul>
  
  <h3>Bug:</h3>
  
  <p>The bug occurs when going back from the Second to the First view using the popgesture. If you pull the second view halfway and then go back to the second view, the navigation title will show "Second View" (as expected).But when you go to the Third view, the title will not change to "Third View". And then on clicking the back button of the Third view, the navbar will get messed up. </p>
  
  <p>Please check out my demo app. Any help explaining why this bug is happening will be appreciated. Thanks!</p>