Changing MainPage between AppShell and NagivationPage breaks app screen.

Hello.
I found an issue of Xamarin.Forms 4.0 on Changing MainPage between AppShell and NagivationPage.

It is very easy to reproduce the issue.

1) Create a Xamarin.Forms 4.0 solution with AppShell Template

2) Add a Content Page (LoginPage.xaml)

3) Change MainPage at App.xaml.cs like this;

    public App()
    {
        InitializeComponent();

        DependencyService.Register<MockDataStore>();
        //MainPage = new AppShell();
        MainPage = new NavigationPage(new LoginPage());
    }

4) Change MainPage in LoginPage like this;

    private void LoginButton_Clicked(object sender, EventArgs e)
    {
        Application.Current.MainPage = new AppShell();
    }

5) Add a MenuItem in AppShell and Add Logout method like this;

private void LogoutMenuItem_Clicked(object sender, EventArgs e) {
Application.Current.MainPage = new NavigationPage(new Views.LoginPage());
}

6) Bulid and run the app

7) “Login and Logout” action makes app screen broken like the attached screen shot.

www.dropbox.com/s/skbgti26v6m2x3u/Screenshot_20190627-181115.png?dl=0

App MainPage is changed like this;

NavigationPage(new Views.LoginPage()) => new AppShell() => NavigationPage(new Views.LoginPage()).

It is very common pattern to implement Login function and I am regarding it must be a XF bug.

It is very easy to reproduce, but I attached my source code for the convenience.

My testing environment is Visual Studio 2019 on Windows 10 Pro and I updated XF 4.0 up to date.

Is there any solution or workaround to solve the issue?

Best regards.