hidesBottomBarWhenPushed = NO not working?

I have a UITabBar in my app, which I'm hiding on the first UIViewController in the first tab by putting this line in the AppDelegate:

// ... in MyAppDelegate.m
firstViewController.hidesBottomBarWhenPushed = YES;

In the firstViewController, the user can push a UIButton that pushes a new UIViewController in the same tab. I'd like for the UITabBar to be visible again when this happens. I'm trying to make it come back like this:

//... in firstViewController.m

secondViewController = [[SecondViewController alloc] init];
secondViewController.hidesBottomBarWhenPushed = NO;
[[self navigationController] pushViewController:secondViewController animated:YES];

Unfortunately, does not bring back the UITabBar. It remains hidden.

How do I properly bring bar the UITabBar after hiding it?

Thanks in advance.