RadioButtonList generates binding warnings in debug window

System.Windows.Data Error: 4 : Cannot find source for binding with reference 'RelativeSource FindAncestor, AncestorType='System.Windows.Controls.ItemsControl', AncestorLevel='1''. BindingExpression:Path=HorizontalContentAlignment; DataItem=null; target element is 'ListBoxItem' (Name=''); target property is 'HorizontalContentAlignment' (type 'HorizontalAlignment')
System.Windows.Data Error: 4 : Cannot find source for binding with reference 'RelativeSource FindAncestor, AncestorType='System.Windows.Controls.ItemsControl', AncestorLevel='1''. BindingExpression:Path=VerticalContentAlignment; DataItem=null; target element is 'ListBoxItem' (Name=''); target property is 'VerticalContentAlignment' (type 'VerticalAlignment')

Here is my markup:

<Window x:Class="Chevron.Dpe.Presentation.Views.CustomUnitsView"
        xmlns="http://schemas.microsoft.com/winfx/2006/xaml/presentation"
        xmlns:x="http://schemas.microsoft.com/winfx/2006/xaml"
        xmlns:actipro="http://schemas.actiprosoftware.com/winfx/xaml/views"
        xmlns:shared="http://schemas.actiprosoftware.com/winfx/xaml/shared"
        xmlns:views="clr-namespace:Chevron.Dpe.Presentation.Views"
        Title="Custom Units"
        Width="700"
        Height="450"
        WindowStartupLocation="CenterOwner">

    <DockPanel>
        <StackPanel Margin="3" HorizontalAlignment="Center" DockPanel.Dock="Bottom" Orientation="Horizontal">
            <Button Width="50" Margin="3" Click="OkClick" Content="OK" />
            <Button Width="50" Margin="3" Click="CancelClick" Content="Cancel" />
            <shared:PopupButton Width="105" Margin="3" Content="Default this to..." DisplayMode="Merged">
                <shared:PopupButton.PopupMenu>
                    <ContextMenu>
                        <MenuItem Command="{Binding Path=BaseOnCommand}" CommandParameter="Field" Header="Field" />
                        <MenuItem Command="{Binding Path=BaseOnCommand}" CommandParameter="Metric" Header="Metric" />
                        <MenuItem Command="{Binding Path=BaseOnCommand}" CommandParameter="Si" Header="Si" />
                    </ContextMenu>
                </shared:PopupButton.PopupMenu>
            </shared:PopupButton>
        </StackPanel>
        <Border Margin="3">
            <ScrollViewer ScrollViewer.HorizontalScrollBarVisibility="Disabled" ScrollViewer.VerticalScrollBarVisibility="Auto">
                <ItemsControl BorderBrush="DarkSlateGray" BorderThickness=".5" ItemsSource="{Binding Path=DomainRows}">
                    <ItemsControl.ItemsPanel>
                        <ItemsPanelTemplate>
                            <actipro:AnimatedWrapPanel />
                        </ItemsPanelTemplate>
                    </ItemsControl.ItemsPanel>
                    <ItemsControl.ItemTemplate>
                        <DataTemplate>
                            <StackPanel Orientation="Horizontal">
                                <TextBlock Width="90" Margin="3" Padding="2" Text="{Binding Path=Description}" />
                                <shared:RadioButtonList Width="100"
                                                        Margin="3"
                                                        BorderBrush="#FF828790"
                                                        BorderThickness="1"
                                                        DisplayMemberPath="ShortName"
                                                        ItemsSource="{Binding Path=Units}"
                                                        SelectedItem="{Binding Path=SelectedUnit}" />
                            </StackPanel>
                        </DataTemplate>
                    </ItemsControl.ItemTemplate>
                </ItemsControl>
            </ScrollViewer>
        </Border>
    </DockPanel>

</Window>