User is not part of parent group

I have below scenario and I am facing a weird issue.
1. testUser is a member of GroupB. if I execute isusermemberofgroup(ri!testUser ,ri!GroupB) it returns me true.
2. GroupA is member group of GroupB if I execute getmembergroups(groupA) it returns me the id of groupA
3. So from this hierarchy testUser should also be the member of GroupA. But I can't see GroupA in Group Section of a user, neither I see the user in a group in designer mode. also
isusermemberofgroup(ri!testUser ,ri!GroupA) expression returns me true

OriginalPostID-267849