Hi Markus,
This is by design. The cell renderer class internally calls style.FormattedText = ControlText to determine the underlying cell value for the display text. This happens before the CurrentCellValidate event is raised and ensures the ControlValue for the renderer is up to date.
Please see the follwing forum thread:
http://www.syncfusion.com/Support/Forums/message.aspx?&MessageID=20084Regards,
Jisha