title: PopToViewController with modals
body: <p>I am currently experimenting with PopToViewController and noticed that if I have the following scenario I get null back from the method:</p>
  
  <p>Navigation Stack</p>
  
  <p>UIViewController1 - position 0 <br/>
  UIViewController2 <br/>
  UIViewController3 <br/>
  UIViewController4 <br/>
  UIViewController5 presented Modally <br/></p>
  
  <p>I get an event triggering a pop back to UIViewController1.  When I call NavigationController.PopToViewController from UIViewController1, the return value is null but the views are removed from the navigation stack but the modal stays open.  I also don't appear to be getting any of the lifecycle events for the UIViewControllers that are removed.</p>
  
  <p>Is this desired behaviour or documented anywhere? I can understand the modal remaining open but I don't get why the PopToViewController method would return null.  </p>
  
  <p>The ViewController I am popping back to is definitely in the Navigation Stack. </p>