To reproduce:

AreaSeries areaSeries = new AreaSeries();
areaSeries.DataPoints.Add(new CategoricalDataPoint(13, "Jan"));
areaSeries.DataPoints.Add(new CategoricalDataPoint(20, "Apr"));
areaSeries.DataPoints.Add(new CategoricalDataPoint(15, "Jul"));
areaSeries.DataPoints.Add(new CategoricalDataPoint(16, "Oct"));
this.radChartView1.Series.Add(areaSeries); 

areaSeries.BackColor = Color.Transparent;

areaSeries.CombineMode = ChartSeriesCombineMode.Stack;
AreaSeries areaSeries2 = new AreaSeries();
areaSeries2.DataPoints.Add(new CategoricalDataPoint(15, "Jan"));
areaSeries2.DataPoints.Add(new CategoricalDataPoint(25, "Apr"));
areaSeries2.DataPoints.Add(new CategoricalDataPoint(27, "Jul"));
areaSeries2.DataPoints.Add(new CategoricalDataPoint(18, "Oct"));
this.radChartView1.Series.Add(areaSeries2);
areaSeries2.CombineMode = ChartSeriesCombineMode.Stack;

 The area underneath the transparent one shouldn't be displayed in this case because they are stacked.  There is no area underneath the bottom layer to display. They are each STACKED on top of each other, they should not be layered in front of each other.

Until the feature gets implemented please use the suggested solution here: http://www.telerik.com/support/kb/winforms/details/integrating-panzoom-trackball-and-lassozoom-controllers-in-radchartview

There are three ways in which null values can be handled:

1 . Zero. When this option is used, each null value is replaced with a zero. The data entry is not removed from the data collection. Only its original null/empty value is replaced with zero. 
2 . Gap. This option visually removes the regions for each set of empty(null) points. The data entry is not removed from the data collection. Essentially, it connects the points neighboring the null point (or the collection of empty values).
3 . Drop - this option clips, or visually removes each section/segment, corresponding to a set of empty points/values. 

The trackball does not work well when charting the dxf cad drawing of a circle or more complex shape

would be better for it to have cross hair mode,  as single point mode does not work (as it picks up a massive array of x,y points in the tooltip, making it unmanageable)

Showtrackball = true
SelectionMode = SingleDataPoint

Telerik.Charting namespace exist in the WinForms and the WFP assemblies and one cannot reference both in a single project.

Add Three Line Break Series to RadChartView

Add Point and Figure Series to RadChartView

Add Kagi Series to RadChartView

Add Renko Series to RadChartView

RadChartView should visualize the pan and zoom state of a view through a scroll bar

To reproduce:
- Use HTML- like text formatting in the chart title.
- Export the chart to image.
- The tags are shown in the text.

Workaround:
private void radButton1_Click(object sender, EventArgs e)
{
    radChartView1.ShowTitle = false;

    TextPrimitiveHtmlImpl impl = new TextPrimitiveHtmlImpl();
    TextParams textParams = this.radChartView1.ChartElement.TitleElement.TextParams;
    SizeF size = impl.MeasureOverride(new SizeF(500f, 200), textParams);

    using (MemoryStream stream = new MemoryStream())
    {
        radChartView1.ExportToImage(stream, new Size(500, 500 - (int)size.Height));

        Bitmap bmp = new Bitmap(500, 500);

        using (Graphics g = Graphics.FromImage(bmp))
        {
            g.Clear(Color.White);
            textParams.paintingRectangle = new RectangleF(Point.Empty, size);
            impl.PaintPrimitive(new RadGdiGraphics(g), textParams);
            g.DrawImage(Image.FromStream(stream), 0, size.Height, 500, 500 - size.Height);
        }

        bmp.Save(@"D:\xfile.bmp");
    }

    radChartView1.ShowTitle = true;
}