How to disable highlighting of RibbonGalleryCategory items when scrolling by keyboard

Question

I have a RibbonSplitButton control in a WPF application.

When I scroll through the dropdownlist with the mouse, the highlighting of items follows the mouse. However, when I use the keyboard to scroll the list, every item I key up/down over gets highlighted. It works fine once I press Enter, but it looks odd. How do I disable the highlighting when using the keyboard?

<RibbonSplitButton x:Name="rbsbCategories" Label="Categories" SmallImageSource="Images/ImageCommenceOpenCategories.png">
    <RibbonSplitButton.Resources>
        <DataTemplate x:Key="MyTemplate">
            <RibbonGalleryItem Content="{Binding}" ToolTip="{Binding}" />
        </DataTemplate>
    </RibbonSplitButton.Resources>
    <RibbonGallery MaxColumnCount="1" SelectedItem="{Binding MyModel.SelectedCategory}">
        <RibbonGalleryCategory ItemsSource="{Binding MyModel.Categories}" ItemTemplate="{DynamicResource MyTemplate}" ScrollViewer.VerticalScrollBarVisibility="Auto" ScrollViewer.CanContentScroll="True"/>
    </RibbonGallery>
</RibbonSplitButton>