WPF ItemsControls Not Showing Collection When Using UserControl in DataTemplate

Question

I am trying to use the MVVM model to create a test application. I have Customers and Orders. Now, I want to display Customers list and when the user click on the customer it should display the Order.

It works perfectly when I use the following code:

<StackPanel DataContext="{Binding Path=Customers}">

            <ListBox IsSynchronizedWithCurrentItem="True" ItemsSource="{Binding}">
                <ListBox.ItemTemplate>
                    <DataTemplate>                       
                            <UserControls:CustomerUserControl />                       
                    </DataTemplate>
                </ListBox.ItemTemplate>

            </ListBox>

            <ItemsControl ItemsSource="{Binding Path=Orders}">
                <ItemsControl.ItemTemplate>
                    <DataTemplate>
                        <TextBlock Text="{Binding Path=Name}" />
                    </DataTemplate>
                </ItemsControl.ItemTemplate>
            </ItemsControl>

        </StackPanel>

The problems comes when I replace the Orders Datatemplate to a user control.

<ItemsControl ItemsSource="{Binding Path=Orders}">
                <ItemsControl.ItemTemplate>
                    <DataTemplate>
                        <UserControls:OrderUserControl></UserControls:OrderUserControl>
                    </DataTemplate>
                </ItemsControl.ItemTemplate>
            </ItemsControl>

Now, it only displays the first item in the customer.Orders collection. The OrderUserControl looks like the following:

<StackPanel>        
        <TextBlock Text="{Binding Path=Name}" />
        <TextBlock Text="{Binding Path=Quantity}" />
    </StackPanel>