title: UIWindow's rootViewController Property
body: <p>I noticed that if I create a viewcontroller and add its view as a subview of window (a UIWindow), the display is incorrect. For some reason, my viewcontroller is displayed 40 points to the top (the same height as the status bar).</p>
  
  <p>If I set the view controller to be the window's rootViewController, it displays fine.</p>
  
  <p>However, if I put this viewcontroller inside a UINavigationController, I don't have to set the rootViewController property and everything works fine. </p>
  
  <p>What's going on?</p>
  
  <p>I need to know what UINavigationController is doing, because I'm writing a controller of controllers too, and need this behavior.</p>