title: Black stripe when tool bar hide iOS
body: <p>I have View with MKMapView:  </p>
  
  <pre><code>- (void)viewDidLoad
  {
     [super viewDidLoad]; 
     self.navigationController.toolbarHidden = NO;
  
     /* code of MKMapView ...*/
  }
  
  - (void)viewWillDisappear:(BOOL)animated
  {
     self.navigationController.toolbarHidden = YES;
  }
  </code></pre>
  
  <p>and when I get out from this view, for a few seconds instead toolBar I see black stripe! What is this?? </p>