Changing the rootViewController of a UIWindow

When my app first loads, I set the `rootViewController` property of my `UIWindow` to `controllerA`. Sometime during my app, I choose to change the `rootViewController` to `controllerB`. The issue is that sometimes when I do a flip transition in `controllerB`, I see `controllerA`'s view behind it. For some reason that view isn't getting removed. Whats even more worrying is that after setting the `rootViewController` to `controllerB`, `controllerA`'s `dealloc` method never gets fired. I've tried removing the subviews of `UIWindow` manually before switching to `controllerB`, that solves the issue of seeing `controllerA`'s views in the background but `controllerA`'s dealloc still never gets called. Whats going on here???? Apples docs say: The root view controller provides the content view of the window. Assigning a view controller to this property (either programmatically or using Interface Builder) installs the view controller’s view as the content view of the window. If the window has an existing view hierarchy, the old views are removed before the new ones are installed. UPDATE Here's the code of my AppDelegate: ``` - (BOOL)application:(UIApplication *)application didFinishLaunchingWithOptions:(NSDictionary *)launchOptions { self.window = [[UIWindow alloc] initWithFrame:[[UIScreen mainScreen] bounds]]; [self showControllerA]; [self.window makeKeyAndVisible]; return YES; } - (void)showControllerA { ControllerA* a = [ControllerA new]; self.window.rootViewController = a; } - (void) showControllerB { ControllerB* b = [ControllerB new]; self.window.rootViewController = b; } ```