Strange focus behavior for simple WPF ItemsControl

Question

I'm seeing strange behavior when it comes to focus and keyboard navigation. In the example below I have a simple ItemsControl that has been templated so that it presents a list of CheckBoxes bound to the ItemsSource.

<ItemsControl FocusManager.IsFocusScope="True"
              ItemsSource="{Binding ElementName=TheWindow, Path=ListOStrings}">
    <ItemsControl.ItemTemplate>
        <DataTemplate>
            <CheckBox Content="{Binding}" />
        </DataTemplate>
    </ItemsControl.ItemTemplate>
</ItemsControl>

For some strange reason the FocusManager.IsFocusScope="True" assignment causes keyboard focus to fail to be set when checking a checkbox via a mouse click and for focus to jump out of the ItemsControl when a check box is checked using the space bar on the keyboard. Both symptoms seem to point to some strange navigation happening when the checkbox is checked but I'm having a hard time getting to the bottom of it.

This problem occurs if I set any parent element up the visual tree as a focus scope using this method. If I remove the FocusManager.IsFocusScope="True" then the problems go away. Unfortunately I'm seeing this problem in a larger project where I cannot just remove these focus scopes without worrying about other focus related consequences.

Could somebody explain to me the strange behavior I'm seeing? Is this a bug or am I just completely missing something?