dovecot - Aug 2008 - dovecot bug - kevent(EV_DELETE, 9)

Sorry for my english.

FreeBSD 7.0-STABLE
dovecot-1.1.2_1 (from ports with LDAP)
AD LDAP ?? Win 2003 SP2 (work via GK)
CPU 2xIntel XEON
NFS not used

LDAP part of dovecot.conf (if you need all file, l'll send it):
auth default {
mechanisms = plain login 
    passdb ldap { 
            args = /usr/local/etc/dovecot-ldap.conf 
        } 

        userdb ldap { 
            args = /usr/local/etc/dovecot-ldap.conf 
        } 
        user = nobody 
        count = 1 
        ssl_require_client_cert = no 
        ssl_username_from_cert = no 

        #Postfix Auth 
        socket listen { 
            client { 
                path = /var/spool/postfix/private/auth 
                mode = 0660 
                user = postfix 
                group = postfix 
            } 
        } 
}

Whole dovecot-ldap.conf:
hosts = 192.168.8.5:3268 192.168.8.6:3268
dn = CN=SomeUser,OU=SomeOU,DC=domain,DC=ru 
dnpass = password 
tls = no 
debug_level = 0 
auth_bind = yes 
ldap_version = 3 
base = DC=domain,DC=ru 
deref = never 
scope = subtree 
user_filter =
(&(mail=%u)(objectclass=user)(memberOf=CN=Mail,OU=SomeOU,DC=domain,DC=ru))
pass_filter =
(&(mail=%u)(objectclass=user)(memberOf=CN=Mail,OU=SomeOU,DC=domain,DC=ru))
default_pass_scheme = CRYPT

My problem.

dovecot works fine with AD! but i have this in logs (This not nice,
but no more):
Aug 14 02:21:03 somecomp dovecot: auth(default): LDAP: Connection lost to LDAP
server, reconnecting
Aug 14 02:21:03 somecomp dovecot: auth(default): kevent(EV_DELETE, 9) failed:
Bad file descriptor
Aug 14 02:36:04 somecomp dovecot: auth(default): LDAP: Connection lost to LDAP
server, reconnecting
Aug 14 02:36:04 somecomp dovecot: auth(default): kevent(EV_DELETE, 9) failed:
Bad file descriptor
Aug 14 02:51:04 somecomp dovecot: auth(default): LDAP: Connection lost to LDAP
server, reconnecting
Aug 14 02:51:04 somecomp dovecot: auth(default): kevent(EV_DELETE, 9) failed:
Bad file descriptor
Aug 14 03:06:05 somecomp dovecot: auth(default): LDAP: Connection lost to LDAP
server, reconnecting
Aug 14 03:06:05 somecomp dovecot: auth(default): kevent(EV_DELETE, 9) failed:
Bad file descriptor
Aug 14 03:21:05 somecomp dovecot: auth(default): LDAP: Connection lost to LDAP
server, reconnecting
Aug 14 03:21:05 somecomp dovecot: auth(default): kevent(EV_DELETE, 9) failed:
Bad file descriptor
Aug 14 03:36:06 somecomp dovecot: auth(default): LDAP: Connection lost to LDAP
server, reconnecting
Aug 14 03:36:06 somecomp dovecot: auth(default): kevent(EV_DELETE, 9) failed:
Bad file descriptor

docecot was launched with debug_level = -1 in dovecot.conf. If you
need this log (it's very big) - i send it too. But i don't see in it
something new (dovecot check connection when it lost and succesefully
reconnecting to AD LDAP).

I want to know:
What this event means?
Can i fix it and what to fix?

> dovecot works fine with AD! but i have this in logs (This not nice,
> but no more):
> Aug 14 02:21:03 somecomp dovecot: auth(default): LDAP: Connection
> lost to LDAP server, reconnecting
> Aug 14 02:21:03 somecomp dovecot: auth(default):
> kevent(EV_DELETE, 9) failed: Bad file descriptor 
> Aug 14 02:36:04 somecomp dovecot: auth(default): LDAP: Connection
> lost to LDAP server, reconnecting 
> Aug 14 02:36:04 somecomp dovecot: auth(default):
> kevent(EV_DELETE, 9) failed: Bad file descriptor 
> Aug 14 02:51:04 somecomp dovecot: auth(default): LDAP: Connection
> lost to LDAP server, reconnecting 
> Aug 14 02:51:04 somecomp dovecot: auth(default):
> kevent(EV_DELETE, 9) failed: Bad file descriptor 
> Aug 14 03:06:05 somecomp dovecot: auth(default): LDAP: Connection
> lost to LDAP server, reconnecting 
> Aug 14 03:06:05 somecomp dovecot: auth(default):
> kevent(EV_DELETE, 9) failed: Bad file descriptor 
> Aug 14 03:21:05 somecomp dovecot: auth(default): LDAP: Connection
> lost to LDAP server, reconnecting 
> Aug 14 03:21:05 somecomp dovecot: auth(default):
> kevent(EV_DELETE, 9) failed: Bad file descriptor 
> Aug 14 03:36:06 somecomp dovecot: auth(default): LDAP: Connection
> lost to LDAP server, reconnecting 
> Aug 14 03:36:06 somecomp dovecot: auth(default):
> kevent(EV_DELETE, 9) failed: Bad file descriptor
I understand. Windows 2003 close idle connections every 15 minutes (that policy
set by default
in any windows 2003 server) and dovecot reconnects with this error.

Unfortunately dovecot haven't "keep-alive" parameter to keep
connection to LDAP alive (not idle). :(
And only that parameter can resolve my problem.