title: presentingViewController is nil when using presentViewController:animated:completion: in iOS 8
body: <p>Wondering if anyone else has encountered this issue recently...</p>
  
  <p>For one of my view controllers , only on iOS 8, after calling <code>presentViewController:animated:completion:</code>, the presented view controller has <code>self.presentingController</code> as nil. It is fine on iOS7, and also does not happen on another view controller.</p>
  
  <p>The <a href="https://developer.apple.com/library/ios/Documentation/UIKit/Reference/UIViewController_Class/index.html#//apple_ref/occ/instp/UIViewController/presentingViewController" rel="noreferrer">documentation</a> says that it should be set, as long as the presented view controller was presented modally. Given it works in iOS 7, could this be an iOS 8 bug?</p>
  
  <p>I've been able to get around it using a view container containment approach, but it would be good if someone has seen this before and knows the root cause that triggered this behaviour. </p>
  
  <p>thanks</p>