netatalk, samba + osx file ownership problem

I am having a few problems with file permissions.

We a file server serving nfs v4 - and an ubuntu server which mounts it that runs netatalk v3.0.1

Seems that when a file is created via a NFS client, then modified by the

afp server, the perms go a bit screwy.

for example....

fred creates test.doc in the 'store' share, on a client with nfs it has these permissions

-rw-rw---- 1 fred testgroup 12 Dec 12 11:30 test.doc

When John edits it with a mac mounted via afp or smb it changes it to:

-rw-rw---- 1 john testgroup 12 Dec 12 11:32 test.doc

So test.doc when modified by a client with an afp or smb mount now belongs to john

Why does this happen?

here is a copy of my afp.conf

******************************************************************************** *********************************

### Netatalk 3.0.1 config param's

# Global Parameters

[Global]

log file = /var/log/netatalk/netatalk.log

#log level = default:debug

mimic model = RackMac

#uam list = uams_dhx.so, uams_dhx2.so, uams_randum.so, uams_gss.so

uam list = uams_dhx2.so, uams_gss.so

k5 keytab = /etc/krb5.keytab

k5 service = afpserver

k5 realm = sumat.blah

# Volume default parameters

[default_for_all_vol]

#file perm = 0664

directory perm = 0774

unix priv = yes

convert appledouble = yes

cnid scheme = dbd

dircachesize = 131072

# File system mounts

[Homes]

basedir regex = /home

home name = home/$u

valid users = @blah

cnid scheme = tdb

ea = none

[store]

name = store

path= /store

file perm = 0640

directory perm = 0755

valid users = @blah

cnid scheme = tdb

ea = auto

******************************************************************************** *********************************

This also happens to macs connect to a samba share so I'm wondering if I have to modify something in osx (10.8.2) ??