Programmer - TemplateBindings in Custom Controls

Programmer Question

I'm just mucking about with custom controls in silverlight and for the life of me i can't get the TemplateBindings to work. Can someone give this reduced version a once over to see if I'm missing something.

So my ControlTemplate in the generic.xaml looks like

<ResourceDictionary xmlns="http://schemas.microsoft.com/winfx/2006/xaml/presentation"
    xmlns:x="http://schemas.microsoft.com/winfx/2006/xaml"
    xmlns:local="clr-namespace:NumericStepperControl;assembly=NumericStepperControl">
    <Style TargetType="local:NumericStepper">
        <Setter Property="Template">
            <Setter.Value>
                <ControlTemplate TargetType="local:NumericStepper">
                    <Grid>
                        <Grid.ColumnDefinitions>
                            <ColumnDefinition />
                            <ColumnDefinition />
                        </Grid.ColumnDefinitions>

                        <Border Grid.Column="0" BorderBrush="Black" BorderThickness="2"  Width="50" Height="30">
                            <TextBlock Width="50" Height="30" Text="{TemplateBinding Value}" />
                        </Border>
                    </Grid>
                </ControlTemplate>
            </Setter.Value>        
        </Setter>
    </Style>
</ResourceDictionary>

and my control class looks like:

namespace NumericStepperControl
{
    public class NumericStepper : Control
    {
        public static readonly DependencyProperty ValueProperty = DependencyProperty.Register("Value", typeof(int), typeof(NumericStepper), new PropertyMetadata(20));

        public NumericStepper()
            : base()
        {
            DefaultStyleKey = typeof( NumericStepper );
        }

        public int Value
        {
            get
            {
                return (int)GetValue(ValueProperty);
            }
            set
            {
                SetValue(ValueProperty, value);
            }
        }
    }
}

I'm expecting when this runs the TextBlock will display the number 20. Any ideas as to why this isn't working?

As a side not i have a separate project which contains a ref to the NumericStepperControl assembly and when it runs the controls seem to build correctly.

Edit... after a bit more investigation i have discovered that if i change the type of the Value property to a string that works fine. Why does a text block not just call a toString on whatever is passed into it? Is there a way round this as i can see it happening a lot?