Reports Group totalFields not working

Dear All,

I have a report that is able to generate report Outstanding Purchase Order where
"Document Type"=CONST(Order), Outstanding Amount(LCY)FILTER>0

Its suppose to export to excel with 3 different grouping depending on user options:
1)By Brand
2)By Vendor By Brand
3)By Vendor
-----------------------------------------

Keys I used:
-Brand, Buy-From Vendor No.

For option 1(By Brand) in properties,           GroupTotalFields :=Brand,                                   SORTING(Brand)
For option 2(By Vendor By Brand) in properties, GroupTotalFields := Buy-from Vendor No.,Item Category Code, SORTING(Brand,Buy-from Vendor No.)
For option 3(By Vendor) in properties,          GroupTotalFields := Buy-from Vendor No.,                    SORTING(Brand,Buy-from Vendor No.)

Option1, 3 solved but option 2 it only show me 1 records By Vendor..