Problem can be seen in the following code:

    private void InitializeChart()
    {
      tChart1.Aspect.View3D = false;

      Area area = new Area(tChart1.Chart);

      area.Add(1, 5, Color.Red);
      area.Add(2, 1, Color.Blue);
      area.Add(3, 4, Color.Yellow);
      area.Add(4, 2, Color.Green);

      area.Stairs = true;
    }

Workaround is to override PrepareLegendCanvas, where the problem lies, e.g.

  public class MyArea : Area
  {
    public MyArea(Chart c) : base(c) { }

    protected override void PrepareLegendCanvas(Graphics3D g, int valueIndex, ref Color backColor, ref ChartBrush aBrush)
    {
    }
  }