title: Menu is created, but disappears after navigations
body: <p>I created menu in Xamarin Android application. It is showing on first page, but after PushAsync it disappears. Also after returning to first page it is not showing any more. Here is a code:</p>
  
  <pre><code>public class MainActivity : global::Xamarin.Forms.Platform.Android.FormsAppCompatActivity, IOnMenuItemClickListener
  {
      protected override void OnCreate(Bundle bundle)
      {
          TabLayoutResource = Resource.Layout.Tabbar;
          ToolbarResource = Resource.Layout.Toolbar;
  
          base.OnCreate(bundle);
  
          global::Xamarin.Forms.Forms.Init(this, bundle);
          LoadApplication(new App());
  
          var toolbar = FindViewById&lt;Android.Support.V7.Widget.Toolbar&gt;(Resource.Id.toolbar);
          toolbar.InflateMenu(Resource.Menu.action_menu);
          toolbar.SetOnMenuItemClickListener(this);
      }
  
      public bool OnMenuItemClick(IMenuItem item)
      {
          ...
          return true;
      }
  }
      public App()
      {
          InitializeComponent();
  
          MainPage = new NavigationPage(new MainPage());
      }
  
  public partial class MainPage : ContentPage
  {
      ...
      private async void OnSecondPageClicked()
      {
          await Navigation.PushAsync(new SecondPage());
      }
  }
  </code></pre>
  
  <p>File action_menu.xml:</p>
  
  <pre><code>&lt;?xml version="1.0" encoding="utf-8" ?&gt;
  &lt;menu xmlns:android="http://schemas.android.com/apk/res/android"
    xmlns:local="http://schemas.android.com/apk/res-auto"&gt;
      &lt;item android:id="@+id/item1"
          android:title="new_game"
          android:showAsAction="always"/&gt;
      &lt;item android:id="@+id/item2"
          android:title="help"
          android:showAsAction="always"/&gt;
  &lt;/menu&gt;
  </code></pre>