title: iOS 8 - Screen blank after dismissing view controller with custom presentation
body: <p>When dismissing various view controllers using <code>UIModalPresentationCustom</code>, the screen turns black after the view controller is dismissed, as if all the view controllers had been removed from the view hierarchy.</p>
  
  <p>The transitioning delegate is set properly, the animationControllerForPresentedController is asked for and passed correctly, and the transition is completed once the animation is over. </p>
  
  <p>This exact code works perfectly when compiled with the iOS 7 SDK, but is broken when compiled with iOS 8b5 </p>