title: Right NavBar Button item disappears after pushing view controller
body: <p>So we got a Nav Controller with a UITableView for the RootViewController. Then when the user clicks the table cell, we push an EKEventController onto the Nav stack and display details for  the event represented by the table cell.</p>
  
  <p>I am trying to add a button on the right side, but it does not show up. </p>
  
  <p>I'm adding the button when the user clicks the table cell.</p>
  
  <pre><code>- (void)tableView:(UITableView *)tableView didSelectRowAtIndexPath:(NSIndexPath *)indexPath 
  {  
  
      // Upon selecting an event, create an EKEventViewController to display the event.
      self.detailViewController = [[[EKEventViewController alloc] initWithNibName:nil bundle:nil]autorelease];            
      detailViewController.event = [self.eventsList objectAtIndex:indexPath.row];
  
      detailViewController.allowsEditing = NO;  
      UIBarButtonItem *locationMapViewButtonItem = [[UIBarButtonItem alloc] 
                                                    initWithTitle:@"Map"
                                                            style:UIBarButtonItemStylePlain 
                                                           target:self 
                                                           action:@selector(showMap:)];  
      self.navigationItem.rightBarButtonItem = locationMapViewButtonItem;  
      [locationMapViewButtonItem release];  
      UITableView *eventTableView = [[self.detailViewController.view subviews]objectAtIndex:0];  
      [self.navigationController pushViewController:detailViewController animated:YES];  
  }
  </code></pre>
  
  <p>The right bar button disappears when the EKEvent controller shows up however.</p>