how to create masked date picker control in wpf

I want to add masking to WPF date picker control. I saw that DatePickerTextBox can not be extended any further.

So, I decided a add a interactivity behavior to it. I used following code for this:

Masked date picker class:

public class MaskedDatePicker : DatePicker
    {
    } 

and I created a attached behavior like below:

public class DatePickerTextBoxInputMaskBehavior : Behavior<DatePickerTextBox>
    {
    }

Now in templates I attached the behavior:

<DatePickerTextBox x:Name="PART_TextBox"
                                               Grid.Row="0"
                                               Grid.Column="0"
                                               HorizontalContentAlignment="Stretch"
                                               VerticalContentAlignment="Stretch"
                                               Focusable="{TemplateBinding Focusable}"
                                               Foreground="{TemplateBinding Foreground}"><i:Interaction.Behaviors><cleanPoc:DatePickerTextBoxInputMaskBehavior /></i:Interaction.Behaviors></DatePickerTextBox>

Now every time i open the calender from datepicker application freezes because text changed in DatePickerTextBoxInputMaskBehavior got fired recursively. 

Kindly suggest Where is the issue and How can i add masking to a date picker. I have attached the code for the sample application. Complete code can be found here: https://onedrive.live.com/?cid=1031D83C0E173CE9&id=1031D83C0E173CE9%21105

Please help