CustomPointMarker and RenderPassData

I had no luck, but I don’t know if I did the right thing:
from your SciChart_SeriesWithMetadata example. In the xaml I inserted a dependency property called RenderPD

  <!--  Declare RenderableSeries  -->
        <s:SciChartSurface.RenderableSeries>
            <s:FastLineRenderableSeries x:Name="lineSeries"
                                        StrokeThickness="2"
                                        PaletteProvider="{StaticResource GainLossPaletteProvider}"
                                       >
                <s:FastLineRenderableSeries.PointMarker>
                    <seriesWithMetadata:AnnotatedPointMarker x:Name="AnnotatedPM" RenderPD="{Binding ElementName=lineSeries,Path=CurrentRenderPassData}" Width="5" Height="7" GainMarkerFill="LimeGreen" LossMarkerFill="Red" Stroke="White" StrokeThickness="1"/>
                </s:FastLineRenderableSeries.PointMarker>

In the AnnotatedPointMarker class

   public class AnnotatedPointMarker : BasePointMarker
{

    public IRenderPassData RenderPD
    {
        get { return (IRenderPassData)GetValue(RenderPDProperty); }
        set { SetValue(RenderPDProperty, value); }
    }

    public static readonly DependencyProperty RenderPDProperty =  DependencyProperty.Register("RenderPD", typeof(IRenderPassData), typeof(AnnotatedPointMarker));

I got no errors, but in the draw() method the variable RenderPD is alwasy set to null.

Am I doing something wrong?

Otherwise, (tell me If I have to open a new ticket for this request) I can use a CustomRenderableSeries, but which is the best practice to send metadata to the draw() method?

thanks