title: self.navigationItem.backBarButtonItem.title=@"back" does not work for the next view controller?
body: <p>I know  <code>self.navigationItem.backBarButtonItem.title</code> is set for the next view controller;</p>
  
  <p>In view Controller A:
  when I use</p>
  
  <pre><code>self.navigationItem.backBarButtonItem.title=@"back";
  </code></pre>
  
  <p>it does not work.
  However when</p>
  
  <pre><code>UIBarButtonItem *newBackButton=[[UIBarButtonItem alloc] initWithTitle:@"back" style:UIBarButtonItemStyleDone target:nil action:nil];
  [[self navigationItem] setBackBarButtonItem:newBackButton];
  </code></pre>
  
  <p>it works successfully!
  Why…..</p>