title: nested push animation can result in corrupted navigation bar
body: <p>in one of my viewcontroller, lets say A, I have the following:</p>
  
  <pre><code> OnbViewController *on = [[OnbViewController alloc] initWithNibName:nibName bundle:nil];
          onboardingTutorial.delegate_ = self;
  self.test = on
   UINavigationController *nController = [[UINavigationController alloc] initWithRootViewController:self.test]
  [self presentModalViewController:nController]
  [nController release];
  </code></pre>
  
  <p>then inside OnbViewController I have pushed to the navigationController:</p>
  
  <pre><code>[self.navigationController pushViewController:someViewController];
  </code></pre>
  
  <p>then in didSelectRowForIndexPath: I called a delegate, which is A, inside the delegate function I called I tried to push again by doing:</p>
  
  <pre><code>[self.test pushViewController:someOtherViewController];
  </code></pre>
  
  <p>and then this gives me that error:</p>
  
  <pre><code>nested push animation can result in corrupted navigation bar
  Finishing up a navigation transition in an unexpected state. Navigation Bar subview tree might get corrupted.
     Unbalanced calls to begin/end appearance transitions for &lt;someOtherViewController: 0x6f942e0&gt;.
  </code></pre>
  
  <p>any idea?</p>