iPad Navigation controller in splitview popover frame issue

Question

I put a navigation controller as Split-view root-view controller. When the iPad is in Portrait mode the root view controller is displayed inside a popover controller. Its by default I know....

But My problem is The top of root-view controller is seems hide by popover. See the attched image. In it the home bar-button seems hide a small portion in top.

 RootViewController *objRootViewController = [[RootViewController alloc] init];

    DetailViewController *objDetailViewController = [[DetailViewController alloc] init];


    UINavigationController *rootNavigationController = [[UINavigationController alloc] initWithRootViewController:objRootViewController];


    UINavigationController *detailNavigationController = [[UINavigationController alloc] initWithRootViewController:objDetailViewController];


    UISplitViewController *objSplitViewController = [[UISplitViewController alloc] init];
    [objSplitViewController setDelegate:objDetailViewController];


    [objSplitViewController setViewControllers:[NSArray arrayWithObjects:rootNavigationController,detailNavigationController, nil]];

    self.splitViewController = objSplitViewController;

    [self.window addSubview:self.splitViewController.view];

    [objSplitViewController release];
    objSplitViewController = nil;

    [rootNavigationController release];
    rootNavigationController = nil;

    [detailNavigationController release];
    detailNavigationController = nil;

    [objDetailViewController release];
    objDetailViewController = nil;

    [objRootViewController release];
    objRootViewController = nil;