title: Back button disappears after pushing two views using UINavigationController
body: <p>I'm currently developing an app using a UINavigationController. I set the root view controller to ViewController1 and then push ViewController2 and then ViewController3 in response to button click events.</p>
  
  <p>If I then click the back button from view 3, I'm returned to view 2 but this view has no back button. Interestingly as well, having set titles for each of these views ('View 1', 'View 2' and 'View 3' respectively), if I navigate from view 3 back to view 2 using the back button, the title changes to 'View 1' i.e. the title for the initial view (view 1) - not the title for view 2.</p>
  
  <p>If anyone has any idea what might be going on here, your suggestions are very much appreciated.</p>
  
  <p>Many thanks in advance!</p>
  
  <p>Edit: I use the following code to init the UINavigationController in the app delegate:</p>
  
  <pre><code>self.window = [[UIWindow alloc] initWithFrame:[UIScreen mainScreen] bounds]];
  self.viewController1 = [[ViewController1 alloc] init];
  self.viewController2 = [[ViewController2 alloc] init];
  self.viewController3 = [[ViewController3 alloc] init];
  self.navigationController = [[UINavigationController alloc] initWithRootViewController:viewController1];
  self.window.rootViewController = self.navigationController;
  </code></pre>
  
  <p>I later push view controllers to the UINavigationController on button clicks as follows:</p>
  
  <pre><code>MyAppDelegate *appDelegate = (MyAppDelegate*)[[UIApplication sharedApplication] delegate];
  [self.navigationController pushViewController:appDelegate.viewController2 animated:YES];
  </code></pre>