RibbonGallery shows always 3 columns

  <ribbon:RowPanel >
    <ribbon:ButtonGroup IsEnabled="{Binding IsEnabled}"   >
      <ribbon:SplitButton  Focusable="False" Command="{Binding AddListCommand}" Name="RSB_BulletList" ImageSourceSmall ="{x:Static res:Images.bullets_16x16}" ToolTip="{x:Static res:Text.Bullets}"  >
        <ribbon:RibbonGallery Focusable="False" IsPreviewEnabled="False" ScrollViewer.VerticalScrollBarVisibility="Disabled" MediumVariantColumnCount="4" LargeVariantColumnCount="4" VariantBehavior="NoCollapseNoAutoSize"  >
          <ribbon:GalleryItem  Focusable="False" Tag="None" Click="RibbonGalleryItem_Click" BorderThickness="3" BorderBrush="White" >
              <TextBlock Width="40" Height="40">
                <TextBlock.Background>
                  <ImageBrush  ImageSource="{x:Static res:Images.bulletlist_none_40x40}" />
                </TextBlock.Background>
              </TextBlock>
            </ribbon:GalleryItem>

Hi, i have a problem that there are always 3 columns shown.
Old forum message shows to use the varianbehavior NoCollapseNoAutoSize, but this does not work also.

I tell the gallery to show 4, but it does not work.

What am I doing wrong?