AFP and group permissions

Is there a problem with group permissions when files are shared via AFP? I have a OD folder with RO group permissions and no access for world. When I 'su' as a user in the group on the OD server, it works fine. However, when I make an AFP connection with that same user, the contents of that folder is not available. If I turn on RO for world then it works. Clearly, when the AFP connection is made group permissions are not being used. Can someone tell me what is going on here and how to fix it? TIA.