Spline series is drawn incorrectly in scenarios where the data points are clustered in several spots along the XAxis with large gaps in-between. Sample data: Data Series Sample: datetime / double: 21/01/2011 12:08:00AM / 10.0 21/01/2011 12:09:00AM / 16.0 REASON FOR DECLINATION This is supported out-of-the-box by the new RadChartView.
I have experienced the same sort of issues, to an extend that we cannot use this function at all within the RadChart. We wanted to use it as the linear series is not smooth as the charts that you can find in Office 2007-2010.