access rights for Contact modified

Hi,

A strange issue.
A personal PC with 3 users accounts defined, Mandriva 2008.0

I've created my personal Contact list and a 'shared' Contact list.
That shared contact list is in a special folder.
Access to that folder is set like this : chown root:users 
shared ; 'drwxrws---'

So, I'm not a specialist but I understood that all files created inside that 
folder will get the group id 'users' (something like that).

Unfortunatelly, when I open Kmail and play around Contact (same problem with 
Calendar) the owner of all files inside that folder is modified and belong to 
me. It's like the result of command: chown myself:myself *  

Of course, if I logout and someone else try to use Kontact, these 
shared 'Contact' are no more useable and the application crashes without 
messages.

Do you have a fix or an idea how to solve it?

I apologize if it's not the right mailing list.

Regards,
Alexandre