WPF datagrid allow user to add rows?

I would like my WPF Datagrid that is bound to my observable collection to have the blank row at the bottom so that the user can add more info. I've successfully bound the data, i.e. I can see it.

Why is the 'new' blank row not showing? Here is my xaml declaration:

<UserControl.Resources>
  <CollectionViewSource x:Key="MyItems" Source="{Binding Path=AllItems}">
  </CollectionViewSource>
</UserControl.Resource>

<my:DataGrid HorizontalAlignment="Stretch"
  AutoGenerateColumns="True"
  SelectionUnit="FullRow"
  CanUserAddRows="True"
  CanUserDeleteRows="True"
  DataContext="{StaticResource MyItems}"
  ItemsSource="{Binding}">

PS: I'm using Josh Smith's MVVM implementation. I have also read some SO posts on the issue and they have not helped.

Thanks in advance.

Update 2010-01-14:

When the usercontrol load event occurs, "CanUserAdddRows" is false. I suspect is has something to do with the conditions listed here.