title: RootViewController animation transition, initial orientation is wrong
body: <p>So I followed this thread: <a href="https://stackoverflow.com/questions/7703806/rootviewcontroller-switch-transition-animation">RootViewController Switch Transition Animation</a> to transit the window.rootViewController from A to B to C. Code looks like this:</p>
  
  <pre><code>[UIView transitionWithView:self.window 
                    duration:0.5 
                     options: UIViewAnimationOptionTransitionFlipFromLeft 
                  animations:^{
                                 self.window.rootViewController = newViewController;
                  } 
                  completion:nil];
  </code></pre>
  
  <p>The problem is my app shall only support landscape, but during the rootViewController transition, the new view controller appears in portrait mode than quickly rotate to landscape mode.</p>
  
  <p>I'm sure that:</p>
  
  <ol>
  <li>I've set UISupportedOrientation to landscape (home button right)</li>
  <li>for each viewcontroller, in the shouldAutoRotateToOrientation method, I set only for landscape</li>
  </ol>
  
  <p>What could be the other reason?</p>