Dovecot Master User Authentication Fails

Question

I am having trouble to set master user authentication with dovecot. Here is 'dovecot -n' output:

    [root@posta ~]# dovecot -n
# 1.1.20: /etc/dovecot.conf
# OS: Linux 2.6.18-238.12.1.el5 x86_64 CentOS release 5.6 (Final)
log_path: /var/log/dovecot.log
protocols: pop3s imaps imap
ssl_cert_file: /ssl/artvin.edu.tr.crt
ssl_key_file: /ssl/artvin.edu.tr.key
login_dir: /var/run/dovecot/login
login_executable(default): /usr/libexec/dovecot/imap-login
login_executable(imap): /usr/libexec/dovecot/imap-login
login_executable(pop3): /usr/libexec/dovecot/pop3-login
mail_uid: 500
mail_gid: 500
mail_location: maildir:/%Lh/Maildir/:INDEX=/%Lh/Maildir/
mail_executable(default): /usr/libexec/dovecot/imap
mail_executable(imap): /usr/libexec/dovecot/imap
mail_executable(pop3): /usr/libexec/dovecot/pop3
mail_plugins(default): quota imap_quota zlib
mail_plugins(imap): quota imap_quota zlib
mail_plugins(pop3): quota zlib
mail_plugin_dir(default): /usr/lib64/dovecot/imap
mail_plugin_dir(imap): /usr/lib64/dovecot/imap
mail_plugin_dir(pop3): /usr/lib64/dovecot/pop3
pop3_client_workarounds(default):
pop3_client_workarounds(imap):
pop3_client_workarounds(pop3): outlook-no-nuls oe-ns-eoh
lda:
  postmaster_address: root
  auth_socket_path: /var/run/dovecot/auth-master
  mail_plugins: cmusieve quota
  sieve_global_path: /var/vmail/sieve/dovecot.sieve
  log_path: /var/log/sieve.log
auth default:
  mechanisms: plain login
  default_realm: artvin.edu.tr
  user: vmail
  master_user_separator: *
  debug: yes
  debug_passwords: yes
  passdb:
    driver: ldap
    args: /etc/dovecot-ldap.conf
  passdb:
    driver: passwd-file
    args: /etc/dovecot-passwd.masterusers
    pass: yes
    master: yes
  userdb:
    driver: ldap
    args: /etc/dovecot-ldap.conf
  socket:
    type: listen
    client:
      path: /var/spool/postfix/dovecot-auth
      mode: 438
      user: postfix
      group: postfix
    master:
      path: /var/run/dovecot/auth-master
      mode: 438
      user: vmail
      group: vmail
plugin:
  quota_warning: storage=85%% /usr/local/bin/dovecot-quota-warning.sh 85
  quota_warning2: storage=90%% /usr/local/bin/dovecot-quota-warning.sh 90
  quota_warning3: storage=95%% /usr/local/bin/dovecot-quota-warning.sh 95
  quota: maildir
  quota_rule: *:storage=100M
  expire: Trash 7 Trash/* 7 Junk 30
  expire_dict: proxy::expire
  auth_socket_path: /var/run/dovecot/auth-master
  sieve: /var/vmail/sieve/%Ld/%Ln/dovecot.sieve
dict:
  expire: db:/var/lib/dovecot/expire/expire.db

the problem is when I try to login with master user via imapsync authentication failed: Here is dovecot log with failed authentication:

dovecot: Jul 04 15:46:10 Info: auth(default): client in: AUTH   1       PLAIN   service=imap    lip=xxx.xxx.xxx.xxx       rip=xxx.xxx.xxx.xxx      lport=143       rport=39432
dovecot: Jul 04 15:46:10 Info: auth(default): client out: CONT  1
dovecot: Jul 04 15:46:10 Info: auth(default): client in: CONT   1       cmR1cmFuAHppbWJyYUBhcnR2aW4uZWR1LnRyAEFxMXN3MmRlNA==
dovecot: Jul 04 15:46:10 Info: auth(default): passwd-file(zimbra@example.com,xxx.xxx.xxx.xxx,master): lookup: user=zimbra@example.com file=/etc/dovecot-passwd.masterusers
dovecot: Jul 04 15:46:10 Info: auth(default): passdb(zimbra@example.com,xxx.xxx.xxx.xxx,master): Master user logging in as test@example.com
dovecot: Jul 04 15:46:10 Info: auth(default): ldap(test@example.com,xxx.xxx.xxx.xxx): bind search: base=o=domains,dc=example,dc=com filter=(&(objectClass=mailUser)(accountStatus=active)(enabledService=mail)(enabledService=imap)(|(mail=rduran@artvin.edu.tr)(&(enabledService=shadowaddress)(shadowAddress=test@example.com))))
dovecot: Jul 04 15:46:10 Info: auth(default): ldap(test@example.com,xxx.xxx.xxx.xxx): result: objectClass(?unknown?)= mail(?unknown?)= sn(?unknown?)= uid(?unknown?)= storageBaseDirectory(?unknown?)= mailMessageStore(?unknown?)= homeDirectory(?unknown?)= mtaTransport(?unknown?)= enabledService(?unknown?)= mailForwardingAddress(?unknown?)= cn(?unknown?)= accountStatus(?unknown?)= userPassword(?unknown?)= mailQuota(?unknown?)=
dovecot: Jul 04 15:46:10 Info: auth(default): ldap(test@example.com,xxx.xxx.xxx.xxx): invalid credentials (given password: mypass)
dovecot: Jul 04 15:46:11 Info: auth(default): new auth connection: pid=5873
dovecot: Jul 04 15:46:12 Info: auth(default): client out: FAIL  1       user=test@example.com
dovecot: Jul 04 15:46:12 Info: imap-login: Disconnected (auth failed, 1 attempts): user=<test@example.com>, method=PLAIN, rip=xxx.xxx.xxx.xxx, lip=xxx.xxx.xxx.xxx

master user "zimbra" is in "/etc/dovecot-passwd.masterusers". The problem is dovecot try to authenticate ldap user "example" with the master users password and fails.