[Samba] winbind users get lost sometimes

[Nicola Mersi]

I use samba and winbind under linux in a NT4 domain.
I've set pam to use winbind for authentication. Every NT domain user has 
his home (/home/winnt/j.smith) and can login the machine.
It is going all ok but sometimes, I can't understand why, some users are 
not recognized. If I try getent passwd I see theme but if I try to login 
(or su) the user I receive the message that the user does not exist.
The problem appears randomly for 1 or 2 users of 100.
Is there a way to force a sync of the users, and why I see the user with 
getent but I can't login that user?

Here is the global section of my smb.conf

[global]

    workgroup = DOMINIO_NT
    netbios name = GOLIA
    server string = Samba Server %v

    printcap name = cups
    load printers = yes
    printing = cups
    printer admin = @assistenza

    log file = /var/log/samba/log.%m

    max log size = 50

    hosts allow = 10.0.0. 127.

    map to guest = bad user

    security = domain

    password server = server_nt roma
    encrypt passwords = yes
    smb passwd file = /etc/samba/smbpasswd

   username map = /etc/samba/smbusers
   winbind uid = 10000-20000
   winbind gid = 10000-20000
   winbind separator = +
   winbind use default domain = yes

   winbind cache time = 15
   winbind enum users = yes
   winbind enum groups = yes

   template homedir = /home/winnt/%U

   obey pam restrictions = yes
   template shell = /bin/bash

   socket options = TCP_NODELAY SO_RCVBUF=8192 SO_SNDBUF=8192

   wins server = 10.0.0.11

   dns proxy = no