title: UIStackView in collectionview layout content jumping
body: <p>Using a <code>UIStackView</code> in a view in a <code>UICollectionView</code> all of the cells are the same size until I scroll away from a cell and then back to it. 
  It looks awful like the following image where the top picture is larger than the frame of the screen! </p>
  
  <p><a href="https://i.stack.imgur.com/vTgJ3.png" rel="nofollow noreferrer"><img src="https://i.stack.imgur.com/vTgJ3.png" alt="enter image description here"></a></p>
  
  <p>Here is a view of my constraints:</p>
  
  <p><a href="https://i.stack.imgur.com/3xKac.png" rel="nofollow noreferrer"><img src="https://i.stack.imgur.com/3xKac.png" alt="enter image description here"></a></p>
  
  <p>CollectionView setup as:</p>
  
  <pre><code>let layout: UICollectionViewFlowLayout = UICollectionViewFlowLayout()
  layout.sectionInset = UIEdgeInsets(top: 0, left: 0, bottom: 0, right: 0)
  layout.itemSize = CGSize(width: 60, height: 60)
  layout.estimatedItemSize = CGSize(width: 1, height: 1)
  collectionView = UICollectionView(frame: self.view.frame, collectionViewLayout: layout)
  let nib = UINib(nibName: "SimpleStackCollectionViewCell", bundle: nil);
  collectionView.register(nib, forCellWithReuseIdentifier: "MyCell")
  collectionView?.dataSource = self
  collectionView?.delegate = self
  </code></pre>
  
  <p>And I set up the <code>UICollectionView</code> as:</p>
  
  <pre><code> func collectionView(_ collectionView: UICollectionView, layout collectionViewLayout: UICollectionViewLayout, sizeForItemAt indexPath: IndexPath) -&gt; CGSize {
          return CGSize(width: view.bounds.width, height: 500)
      }
  </code></pre>