Second screen below WebviewScaffold

Using WebviewScaffold with appBar and bottomNavigationBar bugs the Navigation.push.

I'm using the WebviewScaffold as my primary route "/", with two IconButtons inside a Row, in the bottomNavigationBar. Also, using the AppBar inside the WebviewScaffold.
Opening the second page replaces only the AppBar and the BottomNavigationBar, the WebView is still there.

Maybe I'm doing something wrong with the Navigator, I don't know. :/

MaterialApp(
      title: 'Flutter Demo',
      debugShowCheckedModeBanner: false,
      theme: ThemeData(
        primarySwatch: Colors.blue,
      ),
      routes: {
        "/": (_) => WebView(),
      },
    );

... 

class _WebViewState extends State<WebView> {
  
  @override
  Widget build(BuildContext context) {
    return new WebviewScaffold(
      url: "https://www.google.com",
      appBar: AppBar(title: Text("First WebPage")),
      bottomNavigationBar: bottomNavigation(context),
    );
  }

  @override
  void dispose() {
    _flutterWebView.dispose();
    super.dispose();
  }

  /// Buttons
  Row bottomNavigation(context) {
    return Row(
      children: <Widget>[
        IconButton(
            icon: Icon(Icons.list),
            onPressed: () {
              openList(context);
            }),
        IconButton(icon: Icon(Icons.phone_android), onPressed: openNativeScreen)
      ],
      mainAxisAlignment: MainAxisAlignment.center,
    );
  }

  ///Actions
  void openList(BuildContext context) {
    Navigator.push(context, new NavigationRoute(builder: (context) => new ListScreen()));
  }
}

Start by reproducing the sample using WebviewScaffold with its appBar, bottomNavigationBar, and Navigator.push call in openList. Inspect how the scaffold and pushed route are composed; done means the second page displays without the original WebView remaining underneath.