title: Unwanted shadow on Navigation Bar when pushing view controllers
body: <p><strong>Short Question:</strong>
  <img src="https://i.stack.imgur.com/i929N.png" alt="enter image description here"></p>
  
  <p>How to remove shadow in the blue circle when pushing view controllers?</p>
  
  <p><strong>Long Question:</strong>
  My app is like facebook. There is a NewsFeed view, Detail post view, and the Page view. Here is what is in my interface builder: <img src="https://i.stack.imgur.com/VJ9vU.png" alt="interface builder"></p>
  
  <p>The <code>HomeViewController</code> is the NewsFeed view, the <code>DetailPostViewController</code> is the Detail Page View, and the <code>FirstViewController</code> is the Page View. The <code>HomeViewController</code> is embeded to a <code>UINavigationController</code> which is embeded to a <code>UITabBarController</code>.</p>
  
  <p>It is perfectly normal when I push from <code>FirstViewController</code> to <code>DetailPostViewController</code>. (Note that I don't use segue to push, but storyboard ID)
  <img src="https://i.stack.imgur.com/Hx63m.png" alt="enter image description here"></p>
  
  <p>but when I push from <code>DetailPostViewController</code> to <code>FirstViewController</code>, there is a weird shadow on the navigation bar, like overlapping. But I don't want that. (Not using segue, but storyboard ID)
  <img src="https://i.stack.imgur.com/i929N.png" alt="enter image description here"></p>
  
  <p>And this is my code pushing to <code>FirstViewController</code></p>
  
  <pre><code>var vc = self.storyboard?.instantiateViewControllerWithIdentifier("PageViewController") as! FirstViewController
  self.navigationController?.pushViewController(vc, animated: true)
  </code></pre>
  
  <p>How do I make the push from <code>DetailPostViewController</code> to <code>FirstViewController</code> look normal? I tried using segue but it didn't work. Been trying for so long but still no luck. Thanks.</p>