ContextMenu items are not displayed on small screen resolution

I created a sample WPF application that uses the MS ContextMenu with lots of items (~30). The MainWindow.xaml starts like this:

<Window x:Class="ContextMenuDemo.MainWindow"
        xmlns="http://schemas.microsoft.com/winfx/2006/xaml/presentation"
        xmlns:x="http://schemas.microsoft.com/winfx/2006/xaml"
        Title="MainWindow"
        Width="525"
        Height="350">
  <Grid>
    <Label>
      Right Click Here!
      <Label.ContextMenu>
        <ContextMenu>
          <Button Content="Item10" />
          <Button Content="Item11" />
          <Button Content="Item12" />
          <Button Content="Item13" />
          <Button Content="Item14" />
          <Separator />

When I run the application on a monitor with 800x600 screen resolution the context menu - since there is not enough UI realestate to display the full list of items - shows little scroll arrows at the bottom and/or the top to allow navigating to invisible items.

Then I modified the application and changed Window to RibbonWindow, ContextMenu to Actipro ContextMenu and so on. I have also followed the Actipro documentation and added a Menu as the only direct child of the ContextMenu. The ContextMenu items are children of this Menu. Now the MainWindow.xaml starts like this:

<ribbon:RibbonWindow x:Class="ActiproDemo.MainWindow"
                     xmlns="http://schemas.microsoft.com/winfx/2006/xaml/presentation"
                     xmlns:x="http://schemas.microsoft.com/winfx/2006/xaml"
                     xmlns:ribbon="http://schemas.actiprosoftware.com/winfx/xaml/ribbon"
                     Width="525"
                     Height="350"
                     ApplicationName="Actipro Demo">
  <Grid>
    <Label>
      Right Click Here!
      <Label.ContextMenu>
        <ribbon:ContextMenu>
          <ribbon:Menu>
            <ribbon:Button Label="Item10" />
            <ribbon:Button Label="Item11" />
            <ribbon:Button Label="Item12" />
            <ribbon:Button Label="Item13" />
            <ribbon:Button Label="Item14" />
            <ribbon:Separator />
            <ribbon:Button Label="Item20" />

 When I run the application on the same 800x600 screen resolution monitor:

1. Not all the items are visible (Same as MS behavior)
2. There are no scroll arrows at the bottom and/or the top of the menu to allow navigation to invisible items (Not same as MS behavior)

Do you have any recommendation how to get the scroll arrows working with the Actipro ContextMenu?