Image Source in Xaml not working on WinPhone

I have the following code in a Xamarin Form (v1.3.4.6332) Xamarin VS Extension (v3.9.344):

<Image Grid.Row="1" Grid.Column="0">
        <Image.Source>
          <OnPlatform x:TypeArguments="ImageSource">
            <OnPlatform.iOS>
              <FileImageSource File="Icons/AppAlert.png"/>
            </OnPlatform.iOS>
            <OnPlatform.Android>
              <FileImageSource File="appalert.png"/>
            </OnPlatform.Android>
            <OnPlatform.WinPhone>
              <FileImageSource File="Assets/Icons/AppAlert.png"/>
            </OnPlatform.WinPhone>
          </OnPlatform>
        </Image.Source>
      </Image>-->

It works fine on both iOS and Android but the image is never display on the WinPhone. The image is set to content. I have moved the image to the root folder on the WinPhone project and it still does show. I then tried the following code:

<Image x:Name="AlertImage" Grid.Row="1" Grid.Column="0" Source="Assets/Icons/AppAlert.png" />

Again no joy. Finally I put the following code in the code behind file:

AlertImage.Source = Device.OnPlatform(iOS: ImageSource.FromFile("Icons/AppAlert.png"), Android: ImageSource.FromFile("appalert.png"), WinPhone: ImageSource.FromFile("Assets/Icons/AppAlert.png"));

and the image now shows on the WinPhone.

Is this a bug or am I doing something wrong?