Hi Paul,
Thanks for contacting Syncfusion support.
We have created a simple sample to reproduce the reported issue and it is available in the following location. We were unable to reproduce the reported issue in our end. We have checked the reported scenario with integer, double and float values. We have also checked it in DataTable, ObservableCollection and List as underlying DataSource.
Please have a look at the provided sample. If still the issue exists, provide us with a sample that shows this issue or revert us with reproduced issue in above sample. Give us the details on the DataSource that you have used and the underlying type of the quantity column. This will be helpful for us to have a closer look into the problem and fix it.
Regards,
Mohanram A.