Binding Error with ZoomContentControl, sample usage

I've got a simple docking/MDI application where each tab shows an image.  When I tried wrapping each image in a ZoomContentControl, it yielded the error:

System.Windows.Data Error: 4 : Cannot find source for binding with reference 'RelativeSource FindAncestor, AncestorType='ActiproSoftware.Windows.Controls.Navigation.ZoomDecorator', AncestorLevel='1''. BindingExpression:Path=ZoomLevelAnimated; DataItem=null; target element is 'ScaleTransform' (HashCode=3499754); target property is 'ScaleX' (type 'Double')

 However, functionality of the zoom control works as expected.  What might be causing this message to appear?

Some code:

    <Window.Resources>
        <Style x:Key="DocumentItemStyle" TargetType="docking:DocumentWindow">
            <Setter Property="Title" Value="{Binding Title}" />
            <Setter Property="FileName" Value="{Binding Filename}" />
            <Setter Property="ContentTemplate">
                <Setter.Value>
                    <DataTemplate>
                        <navigation:ZoomContentControl IsPanPadVisible="False" IsResetViewButtonVisible="False">
                            <shared:ActiproLogo />
                        </navigation:ZoomContentControl>
                    </DataTemplate>
                </Setter.Value>
            </Setter>
        </Style>
    </Window.Resources>

        <docking:DockSite
                          sampleCommon:DockSiteViewModelBehavior.IsManaged="true" 
                          DocumentItemsSource="{Binding DocumentItems}"
                          DocumentItemContainerStyle="{StaticResource DocumentItemStyle}" >
            <docking:Workspace>
                <docking:TabbedMdiHost />
            </docking:Workspace>
        </docking:DockSite>