[Samba] sambaRefuseMachinePwdChange policy

[Frank]

Hi,
we have a couple of Linux RHEL 5 samba servers in a domain, one as PDC 
and the other as BDC, and both with LDAP backends
samba version is 3.0.28-1
We want pc clients can't change their machine password using 
sambaRefuseMachinePwdChange policy, so we set it to 1 in LDAP
But pc clients still can change their passwords, and we don't see any 
acces to sambaRefuseMachinePwdChange attribute on LDAP logs.
Is it not used in this version yet? Must we do something special to use it?

Thanks in advance.

Frank