To reproduce:

Create a RadChartView, add a ZoomController and set the ShowGrid property to true:

ScatterSeries series = new ScatterSeries();
series.DataPoints.Add(new ScatterDataPoint(5, 5));
series.DataPoints.Add(new ScatterDataPoint(4, 2));
series.DataPoints.Add(new ScatterDataPoint(-1, 3));
series.DataPoints.Add(new ScatterDataPoint(11, 4));
chart.Series.Add(series);


chart.Controllers.Add(new LassoZoomController());
chart.ShowGrid = true;

You will see that the grid is painted outside of the chart area where the points are