title: presentModalViewController does nothing
body: <p>I have a UIViewController (<em>parent</em>) that calls <code>presentModalViewController</code> with another UIViewController (<em>child</em>) on <code>viewDidLoad</code>.</p>
  
  <p>If <em>parent</em> doesn't have a UINavigationController, then <code>presentModalViewController</code> does nothing. If it has a UINavigationController, then <code>presentModalViewController</code> shows <em>child</em> as expected.</p>
  
  <p>Is this the standard behavior of <code>presentModalViewController</code> or is there something else at play here?</p>