XBAP: Binding to object from resource not work?

Question

In “Wpf Browser Application” project. Page:

<Page.Resources>
    <local:SomeClass x:Key="someClass" Value="String from XAML"/>
</Page.Resources>
<StackPanel>
    <TextBox Text="{Binding Source={StaticResource someClass}, Path=Value}" />
</StackPanel>

and class:

internal class SomeClass
{
    public SomeClass()
    {
        Value = "TEST TEXT";
    }
    public string Value{get;set;}
}

When run TextBox is still empty, why?

P.S.

1. Similar desktop WPF application fill TextBox.

2. In VS2008 in design time Texbox is filling.