To reproduce:

Use the following code with RadChartView: 

this.Chart.Series.Add(new LineSeries());


for (int i = 0; i < 50; i++)
{
    if (i == 10)
    {
        this.Chart.Series[0].DataPoints.Add(new CategoricalDataPoint(1));
        continue;
    }


    this.Chart.Series[0].DataPoints.Add(new CategoricalDataPoint(0));
}

this.Chart.ShowGrid = true;

You will see that the point will not be rendered correctly and will be taller than 1.