Creating a Silverlight control that to be used in a DataForm and flags when changed

Question

Hi

I have created a custom control and am trying to use it in a dataform for editing. If I use a standard TextBox, the dataform flags that the data is dirty (it enabled the OK and Cancel button, and displays the *). However, when I use my control, it doesn't. The XAML I'm using is:

<toolkit:DataForm CurrentItem="{Binding Path=CurrentEntity}">
    <toolkit:DataForm.EditTemplate>
        <DataTemplate>
             <toolkit:DataField Label="Value">
                <TextBox Text="{Binding Path=Value, Mode=TwoWay}" />
             </toolkit:DataField>
        </DataTemplate>
    </toolkit:DataForm.EditTemplate>
</toolkit:DataForm>

versus:

<toolkit:DataForm CurrentItem="{Binding Path=CurrentEntity}">
    <toolkit:DataForm.EditTemplate>
        <DataTemplate>
             <toolkit:DataField Label="Value">
                <my:ValueEditor Value="{Binding Path=Value, Mode=TwoWay}" />
             </toolkit:DataField>
        </DataTemplate>
    </toolkit:DataForm.EditTemplate>
</toolkit:DataForm>