title: 2 UICollectionViews in a container view, only one scrolls
body: <p>I have a parent container view with 2 different UICollectionViews children added as subviews. One is at the top of the screen, the other at the bottom. Both scroll horizontally. The problem is that only the collectionview added last (ie at the top of the parent's view hierarchy) can be scrolled - it doesn't matter which one. I have tried adding a table view and a collectionview to the same container, and both are scrollable, so I feel like it should work with two collectionviews.</p>
  
  <p>Any ideas?</p>
  
  <p>class photoTapContainerVC: UIViewController {</p>
  
  <pre><code>var CIP:NSIndexPath!
  
  override func viewDidLoad() {
      super.viewDidLoad()
  
      //  Create the two views used in the container view.
      var photoTapViewVC :photoTapViewController3 = photoTapViewController3(collectionViewLayout: UICollectionViewFlowLayout(), currentIndexPath: CIP)
  </code></pre>
  
  <p>var collectionVC:photoTapCollectionVC = photoTapCollectionVC(collectionViewLayout: UICollectionViewFlowLayout(), currentIndexPath: CIP)</p>
  
  <pre><code>    // Position/display the two views on the container view
      self.addChildViewController(photoTapViewVC)
      self.view.addSubview(photoTapViewVC.view)
      self.addChildViewController(collectionVC)
      self.view.addSubview(collectionVC.view)
  </code></pre>
  
  <p>let photoTapViewCellIdentify = "photoTapViewCellIdentify"</p>
  
  <p>class photoTapViewController3: UICollectionViewController, UICollectionViewDelegateFlowLayout {</p>
  
  <pre><code>init(collectionViewLayout layout: UICollectionViewFlowLayout!, currentIndexPath indexPath: NSIndexPath){
  
      //Sets up the CollectionView and ViewFlowLayout
      super.init(collectionViewLayout:layout)
  
      let collectionView :UICollectionView = self.collectionView!;
      collectionView.frame = CGRectMake(0, 34, 320, 320)
      collectionView.pagingEnabled = true
      collectionView.registerClass(photoTapViewCell2.self, forCellWithReuseIdentifier: photoTapViewCellIdentify)
      self.makeBackHeader()
  
      layout.scrollDirection = UICollectionViewScrollDirection.Horizontal
      layout.itemSize = CGSizeMake(320, 320)
      layout.sectionInset = UIEdgeInsets(top: 0, left: 0, bottom: 0, right: 0)
      layout.minimumInteritemSpacing = 0
      layout.minimumLineSpacing = 0
  
      collectionView.performBatchUpdates({
          collectionView.scrollToItemAtIndexPath(indexPath, atScrollPosition: .CenteredHorizontally, animated: false)
          }, completion: nil)
  }
  </code></pre>
  
  <p>The second viewcontroller is more or less the same, just different x/y coordinates (they do not overlap though).</p>