title: UIKit: [UIViewController mutableChildViewControllers] crash?
body: <p>I recently received a crash report from itunes connect. Actually it's the only crash report I got from thousands of users, yet. It's an iPod4,1 device. Interesting parts are:</p>
  
  <pre><code>Date/Time:       2012-02-27 22:53:27.596 +0800
  OS Version:      iPhone OS 5.0.1 (9A405)
  Report Version:  104
  
  Exception Type:  EXC_CRASH (SIGABRT)
  Exception Codes: 0x00000000, 0x00000000
  Crashed Thread:  0
  
  Last Exception Backtrace:
  0   CoreFoundation                  0x338958bf __exceptionPreprocess + 163
  1   libobjc.A.dylib                 0x303891e5 objc_exception_throw + 33
  2   UIKit                           0x31259749 -[UIViewController mutableChildViewControllers] + 1
  3   UIKit                           0x31259349 -[UINavigationController pushViewController:animated:] + 37
  4   MyApp                           0x000081e5 -[MyListController tableView:didSelectRowAtIndexPath:] (MyListController.m:207)
  5   UIKit                           0x312d3565 -[UITableView _selectRowAtIndexPath:animated:scrollPosition:notifyDelegate:] + 945
  6   UIKit                           0x3134bce7 -[UITableView _userSelectRowAtPendingSelectionIndexPath:] + 159
  </code></pre>
  
  <p>It seems that the crash occurs when a row from a table view is selected, and a new view controller is pushed into navigation. According to my code, the new view controller is created already, so the crash occurred in <code>UINavigationController</code>.</p>
  
  <p>It doesn't look like the fault of the code I wrote. And I wonder if I'm correct on this? How do I debug this problem?</p>