[Samba] smb mount as root, access as non-root. Changed behaviour between samba 3.0.x and 3.4.x?

[Seb James]

Hi List,

I have an appliance ("the client") which mounts a CIFS share from a
Samba server - the Samba server usually runs on an Ubuntu system.

Within the client, the root user executes a mount command like this:

mount.cifs \\UBUNTUSERVER\archive /tmp/Default \
    -o noserverino,user='someuser',pass='somepassword',uid='50',gid='7'

That uid/gid pair belongs to the "lp" user on the client.

Once the share is mounted, a process belonging to another user (lp in
this case) writes data into the share.

When I use Ubuntu 8.04 for the samba server, which ships with Samba
3.0.28, this works.

On Ubuntu 10.04 which contains Samba 3.4.7, I am unable to write to the
share as the "lp" user (though root - the original share-mounter - is
able to).

I'm struggling to find what might have changed (a security improvement?,
an alteration of a default option?), and whether I can work around this
change?

Can anyone offer any suggestions?

regards,

Seb James