Return only members from Google group

I've been retrieving members of Google groups successfully for some time now using this Python code:

for group in groups_list:
        members = service.members()
        member_request = members.list(groupKey=group['email'], maxResults=200, roles='MEMBER')     
        memberEmails = []

        while member_request is not None:
            member_results = member_request.execute()
            member_list = member_results.get('members', [])
            for member in member_list:
                memberEmails.append(member['email'].lower())

            member_request = members.list_next(member_request, member_results)

I noticed a couple of weeks ago that this is returning all group members regardless of their role. I can't figure out if Google changed the API or if I have always been returning all members regardless of role. Either way, I need only to return users with the role of MEMBER and not MANAGER or OWNER. Any ideas are greatly appreciated!