Hi Peter,
Sorry for the inconvenience, we are able to understood the difficulties which you are facing. But unfortunately we are unable to replicate this issue in any of our sample and in any case. Could you please check the below sample?
Sample:
http://www.syncfusion.com/uploads/redirect.aspx?&team=support&file=GroupSummary1553048393.zip If possible could you please replicate the problem in our sample?, that would very help to resolve your problem earlier.
Please let us know if you have any queries.
Thanks,
Rajasekar