dovecot - Nov 2013 - 2.2.6 auth process crash using LMTP and LDAP on director.

I'm upgrading my configuration to use director and lmtp for delivery.
(doveconf -n at end of the mail).
I use the same config for auth on mail backends and see no errors.

My setup seem to work nicely but i have some auth process crashing when
using lmtp protocol.

Everything is working a sexpected then i've got 5-6 errors like this in
logs and a crach of the auth process:

dovecot: lmtp(47269): Error: passdb lookup(_mail_): Disconnected 
unexpectedly
pid 47406 (auth), uid 143: exited on signal 11

Actually, i didn't configure to core dump.

Do you think seting up lmtp protocol to static auth adding something 
like folow will be better for this problem?

protocol lmtp {
   passdb {
     args = proxy=y nopassword=y
     driver = static
   }
}

Please note that my configuration is actually listening on inet fot LMTP
but that the goal is to configure postfix on the same server and switch
to socket, this expain the configuration of the service auth to provide
a socket to postfix.

Here is my director config:

% doveconf -n
# 2.2.6: /usr/local/etc/dovecot/dovecot.conf
# OS: FreeBSD 8.4-RELEASE-p4 amd64
auth_cache_negative_ttl = 0
auth_cache_size = 16 M
auth_mechanisms = plain login
auth_verbose = yes
auth_verbose_passwords = sha1
default_process_limit = 4000
director_mail_servers = 192.168.16.1 192.168.16.2 192.168.16.3
director_servers = 192.168.16.4 192.168.16.5 192.168.16.6
disable_plaintext_auth = no
doveadm_port = 24245
info_log_path = syslog
instance_name = director
lmtp_proxy = yes
mail_debug = yes
managesieve_notify_capability = mailto
managesieve_sieve_capability = fileinto reject envelope 
encoded-character vacation subaddress comparator-i;ascii-numeric 
relational regex imap4flags copy include variables body enotify 
environment mailbox date ihave
passdb {
   args = /usr/local/etc/dovecot/dovecot-ldap.conf.ext
   driver = ldap
}
plugin {
   mail_log_events = delete undelete expunge copy mailbox_delete 
mailbox_rename
   mail_log_fields = uid box msgid size
}
service anvil {
   client_limit = 12003
}
service auth-worker {
   process_min_avail = 10
   user = $default_internal_user
}
service auth {
   client_limit = 16000
   unix_listener /var/spool/postfix/private/auth {
     group = postfix
     mode = 0666
     user = postfix
   }
   unix_listener auth-userdb {
     mode = 0666
     user = $default_internal_user
   }
   user = $default_internal_user
}
service director {
   fifo_listener login/proxy-notify {
     mode = 0666
   }
   inet_listener {
     address = 192.168.16.4
     port = 9090
   }
   unix_listener director-userdb {
     mode = 0600
   }
   unix_listener login/director {
     mode = 0666
   }
}
service doveadm {
   inet_listener {
     port = 24245
   }
}
service imap-login {
   executable = imap-login director
}
service lmtp {
   inet_listener lmtp {
     address = * ::
     port = 24
   }
}
service pop3-login {
   executable = pop3-login director
}
ssl_cert = </etc/ssl/cert/mail.univ-angers.fr.pem
ssl_key = </etc/ssl/cert/mail.univ-angers.fr.key
userdb {
   args = /usr/local/etc/dovecot/dovecot-ldap.conf.ext
   driver = ldap
}
protocol lmtp {
   auth_socket_path = director-userdb
}
protocol doveadm {
   auth_socket_path = director-userdb
}
local 192.168.16.0/24/24 {
   doveadm_password = mysecret
}


Last thing, in my config file, there is only one /24 on local network
but this is another problem.