Rollover modifier issue - bar isn't snapping to points on a second series

Hi All,
Although this issue isn’t currently stopping me doing what I need to do I’m just a tad worried that I’m doing something more fundamental wrong which probably will. Anyway the question…

I have a chart with a DateTime axis to which I add two series (red and blue points) from the code behind as per the code snippet. When I run it both series are displayed correctly but the rollover bar only snaps to the second series points. If a run the mouse over a point from the first series it seems to be acknowledged as the fill colour changes but the rollover doesn’t snap to it.

The method is invoked by a button press on a parent control

public void AddTestDataSeries(double seedvalue)
{ 
    DateTime StartPoint = DateTime.Now;
    DateTime[] Axis = new DateTime[] { StartPoint.AddMinutes(1), StartPoint.AddMinutes(2), StartPoint.AddMinutes(3), StartPoint.AddMinutes(4), StartPoint.AddMinutes(5), StartPoint.AddMinutes(6), StartPoint.AddMinutes(7), StartPoint.AddMinutes(8) };
    double[] Series1 = new double[]{1,2,3,5,7,12,19,37};
    double[] Series2 = new double[]{10,20,30,40,50,60,70,80};

    XyDataSeries<DateTime, double> dataSeries1 = new XyDataSeries<DateTime, double> { SeriesName = "Series1" };
    for (int x = 0; x < Series1.Count(); x++)
    {
        dataSeries1.Append(Axis[x], Series1[x]);
    }
    XyScatterRenderableSeries scatterRenderSeries1 = new XyScatterRenderableSeries();
    scatterRenderSeries1.DataSeries = dataSeries1;
    scatterRenderSeries1.PointMarker = new EllipsePointMarker()
    {
        Fill = Colors.Red,
        Stroke = Colors.White,
        StrokeThickness = 2,
        Width = 10,
        Height = 10,
    };
    this.UserControlSciChartSurface.RenderableSeries.Add(scatterRenderSeries1);

    XyDataSeries<DateTime, double> dataSeries2 = new XyDataSeries<DateTime, double> { SeriesName = "Series2" };
    for (int x = 0; x < Series2.Count(); x++)
    {
        dataSeries2.Append(Axis[x].AddSeconds(30), Series2[x]);
    }
    XyScatterRenderableSeries scatterRenderSeries2 = new XyScatterRenderableSeries();
    scatterRenderSeries2.DataSeries = dataSeries2;
    scatterRenderSeries2.PointMarker = new EllipsePointMarker()
    {
        Fill = Colors.Blue,
        Stroke = Colors.White,
        StrokeThickness = 2,
        Width = 10,
        Height = 10,
    };
    this.UserControlSciChartSurface.RenderableSeries.Add(scatterRenderSeries2);

}

And the XAML is simply

<UserControl
         x:Class="SummaryDrillDownCharting.SummaryDataChartUserControl"
         xmlns="http://schemas.microsoft.com/winfx/2006/xaml/presentation"
         xmlns:x="http://schemas.microsoft.com/winfx/2006/xaml"
         xmlns:mc="http://schemas.openxmlformats.org/markup-compatibility/2006" 
         xmlns:d="http://schemas.microsoft.com/expression/blend/2008" 
         xmlns:s="http://schemas.abtsoftware.co.uk/scichart"  
         mc:Ignorable="d" 
         d:DesignHeight="300" d:DesignWidth="300">

<Grid>
    <s:SciChartSurface x:Name="UserControlSciChartSurface" s:ThemeManager.Theme="Chrome">

        <s:SciChartSurface.XAxis>
            <s:DateTimeAxis GrowBy="0.1, 0.1"/>                
        </s:SciChartSurface.XAxis>

        <s:SciChartSurface.YAxis>
            <s:NumericAxis GrowBy="0.1, 0.1" DrawMajorBands="True"/>
        </s:SciChartSurface.YAxis>

        <s:SciChartSurface.ChartModifier>
            <s:ModifierGroup>
                <s:RolloverModifier IsEnabled="True"></s:RolloverModifier>
            </s:ModifierGroup>
        </s:SciChartSurface.ChartModifier>

    </s:SciChartSurface>
</Grid>

ADDITIONAL INFO: I Just ran the same code changing the scatter to a FastLineRenderableSeries – same problem exists.