Hi Michael,
Thanks for being patience. The following is the sample which demonstrates the GridGroupingControl column with MonthCalender celltype without any issues. Is it possible for you to upload us more details or modify the attached sample to reproduce the issue here? So we can debug the issue as early as possible.
Sample :
GGC_MonthCalenderIssueThanks for your interest in our products and for your time.
Best regards,
Madhan