Messy permissions on afp

Hi there, this may be basic but for now it gives me a headache. A few months back I upgraded my server to 10.5.8 Server but since then I have an issue with permissions of files placed on the fileserver. In ServerAdmin I have set the permissions to owner > admin (r+w) and staff (r+w). On 10.3 Server there were hardly any problems but now new files copied to the server have the client as owner and staff set to read only. I want the admin to be the owner again and staff set to r+w. How can I fix this? I have 10.5.8, 10.6.8 and 10.7.4 clients. TIA.