problem with cyrus-imapd and sendmail

[RJ45]

Hello,
I have a problem with FreeBSD and cyrus-imapd.
I have never been able to solve this.
The problem is intermittent and it happens from time to time after a
system rebooot.

Jun 17 00:00:11 postino sm-mta[201]: h5GM0A7T000201: to=myname at domain.com,
delay=00:00:00, xdelay=00:00:00, mailer=cyrusv2, pri=31024,
relay=localhostv, dsn=4.4.1, stat=Deferred: Connection refused by
localhost

actually looks like the /var/imap/socket/lmtp is not accessible

but this is weird, in fact my cyrus configuration is perfect and
the file permissions are correct, in particular:

srwxrwxrwx  1 root  cyrus  0 Feb  9 09:47 /var/imap/socket/lmtp


This behaviour is unpredictable and it happens after a reboot to the mail
server.

this is my cyrus configuration into sendmail.cf

Mcyrusv2,       P=[IPC], F=lsDFMnqXzA@/:|m,
                S=EnvFromSMTP/HdrFromL, R=EnvToL/HdrToL, E=\r\n,
                T=DNS/RFC822/SMTP,
                U=cyrus:cyrus,
                A=FILE /var/imap/socket/lmtp

(note that I tryed with U=cyrus:cyrus and without it as well)

When this problem happens to me I have to do this modification to solve
it:

Mcyrusv2,       P=/usr/local/cyrus/bin/deliver, F=lsDFMnqXA@/:|m,
                S=EnvFromSMTP/HdrFromL, R=EnvToL/HdrToL,
                E=\r\n, T=DNS/RFC822/SMTP,
                U=cyrus:cyrus,
                A=deliver -e -m $h -- $u

I have to call deliver directly even if this is very ugly, but it works.
If after a few hours I Come back to the lmtp cyrus-sendmail configuration
the system comes back working using /var/imap/socket/lmtp

I really don't know how to solve this.
I am sure my configuration is correct.
I use sendmail + cyrus on many boxes, many flavours of unix, Linux, SGI,
Solaris, but I had this problem only with FreeBSD since version 5.0

Anyone had an experience like mine ?
It seems I can't find a solution and this is really overwhelming
since in this way my mail server si quite unstable.
A Reboot can simply screw the whole mail system.

Could the problem be related to /var/imap/socket/lmtp file and
soft updates ??

I ma actually running latest sendmail + latest cyrus version

thank you very much

Rick