NavigationBar not appearing with TTThumbsViewController in UITabBarController

I'm trying to put a TTThumbsViewController inside a UITabBarController, but when I do, the TTThumbsViewController's NavigationBar doesn't show. There is just blank space where the NavigationBar should be. I've loaded just the TTThumbsViewController by itself, and the NavigationBar loads just fine. I'm sure I've just missed a setting, but I can't figure out what it is.

Here is what I'm doing to create the UITabBarController and the TTThumbsViewController:

- (BOOL)application:(UIApplication *)application didFinishLaunchingWithOptions:(NSDictionary *)launchOptions
{
    self.tabBarController = [[UITabBarController alloc] init];
    ThumbsViewController *thumbsViewController = [[ThumbsViewController alloc] init];
    UITabBarItem *thumbsTabBarItem = [[UITabBarItem alloc] initWithTitle:@"Thumbs" image:[UIImage imageNamed:@"icon.png"] tag:Thumbs];
    thumbsViewController.tabBarItem = thumbsTabBarItem;
    self.tabBarController.viewControllers = [NSArray arrayWithObjects:thumbsViewController, nil];
    self.window.rootViewController = self.tabBarController;
    [self.window makeKeyAndVisible];
    return YES;
}

If you're loading the TTThumbsViewController from a UITabController, you need to create the UINavigationController yourself.

- (BOOL)application:(UIApplication *)application didFinishLaunchingWithOptions:(NSDictionary *)launchOptions
{
    self.tabBarController = [[UITabBarController alloc] init];
    ThumbsViewController *thumbsViewController = [[ThumbsViewController alloc] init];
    UITabBarItem *thumbsTabBarItem = [[UITabBarItem alloc] initWithTitle:@"Thumbs" image:[UIImage imageNamed:@"icon.png"] tag:Thumbs];
    thumbsViewController.tabBarItem = thumbsTabBarItem;

    UINavigationController *navController = [[[UINavigationController alloc] initWithRootViewController:ThumbsViewController] autorelease];

    self.tabBarController.viewControllers = [NSArray arrayWithObjects:navController, nil];
    self.window.rootViewController = self.tabBarController;
    [self.window makeKeyAndVisible];
    return YES;
}