title: childviewcontroller of UINavigationController stored in NSArray crashes on ipad
body: <p>I have code to fetch the perticular childviewcontroller of navigation controller.</p>
  
  <pre><code>NSArray *contllrs = [self.navigationController childViewControllers];
  NSLog(@"controllers : %@",contllrs);
   if([contllrs count]&gt;3)
             [self.navigationController popToViewController:[contllrs objectAtIndex:0] animated:YES];
  </code></pre>
  
  <p>It gives log as</p>
  
  <pre><code>childviewcontrollers : NSHashTable (%@) {
  [3] &lt;abcVC: 0x1dc1d0&gt;
  [4] &lt;defVC: 0x5daf790&gt;
  [7] &lt;efgVC: 0x1724a0&gt;
  [10] &lt;adsfVC: 0x1b14f0&gt;
  [11] &lt;SdfVC: 0x1e2c30&gt;
  }
  </code></pre>
  
  <p>Crashes with </p>
  
  <pre><code>InvalidArgument
  </code></pre>
  
  <p>This works fine with iPad simulator but crashes on iPad</p>