Force user parameter change my directory permissions???

[Jethro Hermans]

Hi everybody,

The "force user" parameter in my smb.conf on a share changes always my 
directory permissions

drwxrws---  2 shareUsr test 4096 Jun 15 10:23 test
Change to
drwxrwx---  2 shareUsr test 4096 Jun 15 10:23 test

After I access the folder "test" the SGID bit is always removed.

"test" is a sub folder in a share called "testshare".
What can I do to avoid that this happens because I will force the user 
on my shares to "shareUsr"?
When I remove the "force user" parameter in the smb.conf, everything 
works fine except that the owner of my sub folders are not named as 
"shareUsr".

[testshare]
        comment = test share
        path = /users/samba/groups/testshare/
        valid users = @testshare
        force user = shareUsr
        writable = yes
        create mask = 0660
        directory mask = 2770
 
Thank you for the help,
Jet