Page.IsBusy does not display spinner in Android ActionBar as of 1.4.4.6387

http://developer.xamarin.com/api/property/Xamarin.Forms.Page.IsBusy/

Prior to 1.4.4.6387, the following code displays a spinner in the ActionBar, but it shows nothing after upgrading. Has this feature been removed?

App.cs

public class App : Application
   {
      public App()
      {
         MainPage = new NavigationPage(new TestPage());
      }
   }
   public class TestPage : ContentPage
   {
      public TestPage()
      {
         Title = "Test Title";
         var button = new Button
         {
            Text = "Busy Button"
         };
         button.Clicked += (s, e) =>
         {
            IsBusy = !IsBusy;
         };
         Content = button;
      }
   }

Styles.xml

<?xml version="1.0" encoding="utf-8" ?>
<resources>
  <style name="TestStyle" parent="@android:style/Theme.Holo.Light.DarkActionBar">    
  </style>
</resources>