Static Binding to Singleton Mysteriously Fails

I have the following singleton class which contains the following property:
public class Manager : INotifyPropertyChanged
{
    public bool IsOnline
    ...

    public static Manager Instance
    ...
}

In the mark-up I am trying to change the color of a button based on this online property:
<Button.Style>
 <Style TargetType="{x:Type Button}">
  <Style.Triggers>
   <DataTrigger Value="True">
    <DataTrigger.Binding>
     <Binding Source="{x:Static storage:Manager.Instance}" Path="IsOnline"/>
    </DataTrigger.Binding>
    <Setter Property="Background" Value="#8000FF00"/>
   </DataTrigger>
  </Style.Triggers>
 </Style>
</Button.Style>

This binding <Binding Source="{x:Static storage:Manager.Instance}" Path="IsOnline"/> fails with the exception:

Cannot convert the value in attribute 'Source' to object of type 'System.Windows.Markup.StaticExtension'.

I have quadruple-checked the "storage" namespace; I know it is both referenced and correct.  The Instance property is static, so I do not understand why this binding would fail. I have similar bindings to static properties all over that work just fine.
Any ideas?

I've built a sample app that does exactly what you're describing, it works with no issues. You can download it here.