Windows Phone: AppBar icons appearing differently on the device

I'm mocking up an app in Expression Blend. The app bar looks fine in Blend, but when I launch the emulator the icon doesn't display properly.

The XAML for the app bar:

    <shell:ApplicationBar x:Name="FavoritesBar" IsVisible="True" Is开发者_如何转开发MenuEnabled="True">
      <shell:ApplicationBarIconButton IconUri="/assets/appbar.favs.rest.png" Text="favorites"/>
  </shell:ApplicationBar>

Below left is the way it is rendered in Expression Blend. Below right is the way it appears in the emulator.

What could I be doing wrong here?

Make sure you have marked the appbar.favs.rest.png as Content in Properties->Build Action.