Hi John,
Thanks for your interest in Syncfusion products.
Please refer to the following sample in which a new basestyle is created with celltype set in gridgroupingcontrol. It works fine.
http://files.syncfusion.com/support/samples/Grid.Windows/7.2.0.20/F80950.zipIf you still sees the issue, try to reproduce it in this sample and provide us. So that we can locate the cause for it and work to provide a better solution.
Regards,
Rajadurai