title: A bug of UIScrollView contentOffset?
body: <p>I set the property <code>isPagingEnabled</code> of a scrollView to <code>true</code>, like this:</p>
  
  <pre><code>let scrollView = UIScrollView(frame: view.bounds)
  scrollView.contentSize = CGSize(width: view.bounds.width * 2, height: 0)
  scrollView.delegate = self
  scrollView.isPagingEnabled = true
  view.addSubview(scrollView)
  </code></pre>
  
  <p>and delegate method:</p>
  
  <pre><code>func scrollViewDidScroll(_ scrollView: UIScrollView) {
      print(scrollView.contentOffset.x)
  }
  </code></pre>
  
  <p>When scrolling the view to the boundary, the console print, as shown in:</p>
  
  <p><a href="https://i.stack.imgur.com/36TIT.png" rel="nofollow noreferrer"><img src="https://i.stack.imgur.com/36TIT.png" alt="enter image description here"></a></p>
  
  <p>and</p>
  
  <p><a href="https://i.stack.imgur.com/HmVAP.png" rel="nofollow noreferrer"><img src="https://i.stack.imgur.com/HmVAP.png" alt="enter image description here"></a></p>
  
  <p>The values in the red box should not be printed out, right?</p>
  
  <p>But, if setting <code>isPagingEnabled</code> to <code>false</code>, the console print is normal.  Is this a bug of <code>UIScrollView</code>?</p>