samba - Aug 2012 - samba won't honour group permissions on my share directory

Hi,

I have a share set up in smb.conf as follows

..
security = user
guest account = ftp

..

[incoming]
comment = Incoming files
path = /var/local/share/incoming
public = yes
guest ok = yes
read only = no
browseable = yes

..

the permissions on the shared directory are set recursively as follows -

drwxrwxr-- root ftp incoming

If I try and write to the share from an anonymous windows login, I get a
warning that I do not have the required permissions.
Looking at the permissions tab on Windows I see that the unix group
'ftp'
only has read privileges. My understanding was that
because the guest account is a member of the 'ftp' group it would get
write
privileges. Evidently this is not the case.

If I set the permissions on 'var/local/share/incoming' to world writable
then this gets round the problem, but I'd still like to know
why using group permissions does'nt seem to work.


Mark