[smb/afp] group permissions executable bit set by default: chmod g-x does not remove

How can I mount on OS X with file permissions perserved? Which turns into, how can natatalk be configured to allow chmod changes and not default to group executable permssions?

Summary:

# -- on OS X in AFP mount (e.g. /Volumes/share) ---
umask 022 # no effect
touch test
stat -f '%Sp' test
# -rw-rwxr--  
# why is the group exec bit set!?

# -- try to change permissions, no luck --
chmod g-x
stat -f '%Sp' test
# -rw-rwxr-- # no error but still g+x

# -- change permissions on local filesystem (or nfs mount) ---
ssh user@NAS chmod g-x /data/share/test
stat -f '%Sp' test
# -rw-rw-r-- # success! permissions reflected within AFP mount

I'd like to expose a share to OS X clients over afp or smb such that file permissions are preserved -- so file permissions on nfs mounts and afp mounts look the same. OS X doesn't do nfs well and I cannot find a way to enable unix extensions for samba, so I'm looking at afp (netatalk).

Files created on AFP mounts always have the group executable bit set. chmod has no affect (chmod g-w, chmod g-x, chmod u+x, ... no change). Howver, AFP mount file permissons do reflect any changes made on the NAS share locally or on NFS mounts.

I think this is similiar to

https://community.netgear.com/t5/Using-your-ReadyNAS/AFP-Mount-Point-Permissions-Solved/m-p/695352#M2505