An excellent question so I decided to move it to the Knowledge Base section!
When you group iGrid by a column, in fact, it is sorted first by this column. The 'sort by value' sort criteria is used by default in this case. Obviously, in the general case it is not what your users need as the combo box cell values may differ a lot from what the users see in the cells. To sort by visible cell texts, we recommend that you use the igSortByCellTextNoCase or igSortByCellTextUseCase sort type for your columns with combo box cells. You can specify this sort type in the AddCol method, or using the ColSortType property:
iGrid1.ColSortType("manager")=igSortByCellTextNoCase
If you do this, iGrid will sort and group its contents like the user expects to see. This also directly concerns your question - the internal logic of iGrid will display combo box cell texts instead of their values in the group rows created automatically in this case.