Running the following code and opening the Data tab demonstrates the issue:


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

      CultureInfo ci = new CultureInfo("en-US");
      Thread.CurrentThread.CurrentCulture = ci;
      Thread.CurrentThread.CurrentUICulture = ci;

      DateTime now = DateTime.Now;
      Line line = new Line(tChart1.Chart);
      line.TreatNulls = TreatNullsStyle.DoNotPaint;
      Random rnd = new Random();
      line.DateTimeFormat = "yyyy-MM-d HH:mm:ss";
      line.ValueFormat = "0.###E+0";
      tChart1.Axes.Bottom.Labels.Angle = 90;
      tChart1.Axes.Bottom.Labels.DateTimeFormat = line.DateTimeFormat;

      line.DefaultNullValue = double.NaN;

      for (int i = 0; i < 50; i++)
      {
        now = now.AddMinutes(5);
        if (i % 5 == 0)
          line.Add(now, double.NaN, Color.Transparent);
        else
          line.Add(now, rnd.NextDouble());
      }
    }