[Samba] What does "ldap passwd sync" do?

[Anthony Linux]

Question regarding what the smb.conf line ldap passwd sync = Yes actually does.

I have a lab with mixed Win2k and RH9 computers running Samba 3 and
OpenLdap.  Right now we're having a problem with password expiration. 
Samba is working just fine and when a user changes their password, the
date changes as well.

But for Linux, however the password is being changed is not updating
the shadowLastChange parameter.  So even though the users are
successfully changing their passwords (though Windows), the Linux
boxes are denying access due to that parameter not being set.

So after saying all that, I am trying to get a handle on what "ldap
passwd sync" enables so that I can figure out if this is a bug, Samba
config problem, LDAP config problem, script issue, or PAM problem.

Thanks in advance,
Anthony