show bugs in iOS 18

I used tabBarItem & UITabBarController create a demo app. then I set every pages backgroudcolor as red. when I change to every pages withing the tabBarItem at bottom. the page's background color highlight every time. I don't know why. Is this the new UIKit's bug?

func scene(_ scene: UIScene, willConnectTo session: UISceneSession, options connectionOptions: UIScene.ConnectionOptions) {
    // Use this method to optionally configure and attach the UIWindow `window` to the provided UIWindowScene `scene`.
    // If using a storyboard, the `window` property will automatically be initialized and attached to the scene.
    // This delegate does not imply the connecting scene or session are new (see `application:configurationForConnectingSceneSession` instead).
    guard let scene = (scene as? UIWindowScene) else { return }
    
    let a = UINavigationController(rootViewController: AViewController())
    let b = UINavigationController(rootViewController: BViewController())
    let c = UINavigationController(rootViewController: CiewController())
    
    a.tabBarItem = UITabBarItem(title: "AAA", image: nil, selectedImage: nil)
    b.tabBarItem = UITabBarItem(title: "BBB", image: nil, selectedImage: nil)
    c.tabBarItem = UITabBarItem(title: "CCC", image: nil, selectedImage: nil)
            
    let tabbarVc = UITabBarController()
    tabbarVc.viewControllers = [a,b,c]
    
    window?.backgroundColor = .clear
    window?.rootViewController = tabbarVc
    window?.makeKeyAndVisible()
}

import UIKit

class AViewController: UIViewController {

override func viewDidLoad() {
    super.viewDidLoad()
    
    self.view.backgroundColor = .red

    // Do any additional setup after loading the view.
}

}

show bugs in iOS 18
 
 
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