getent group shows me twice user id in a group

[Allen Chen]

Hi, there

I have a Linux Samba PDC file server with a separate ldap machine backend.
Every thing works perfect. but the problem is that when I do a command 
on the samba server:
      # getent group | grep 1033
It gives me:
      gname:x:1033:usr1,usr2,usr1,usr2,usr3
Some of the user ids show up twice. Why?
I checked ldap database and found that usr1,usr2 and usr3 show up only 
once in memberUid.
All of them do not exist in /etc/passwd and /etc/group files.

Software used:
RedHat ES v4  2.6.9-5.ELsmp
Samba 3.0.22 (compiled)

My nsswitch.conf on samba server looks like:
passwd:     files ldap
shadow:    files ldap
group:       files ldap
hosts:        files dns
bootparams: nisplus [NOTFOUND=return] files
ethers:       files
netmasks:  files
networks:  files
protocols:  files ldap
rpc:           files
services:    files ldap
netgroup:   files ldap
publickey:  nisplus
automount: files ldap
aliases:       files nisplus



Thanks in advance.

Allen