occasional delays in lmtpd

[Kjetil Torgrim Homme]

we're running Cyrus 2.2.12 on RHEL3U7.  about once a day (typically peak
hours), we have a problem with lmtpd just "hanging":

Jul  6 13:36:27 mail-imap3 lmtpunix[1578]: executed
Jul  6 13:55:08 mail-imap3 lmtpunix[1578]: accepted connection
Jul  6 13:55:08 mail-imap3 lmtpunix[1578]: lmtp connection preauth'd as postman

note the 18 minute delay.  during this time, there are no deliveries to
this Cyrus.

at this time, there's about 70% idle CPU and 6 GiB free RAM, so it
shouldn't be resource constrained.  IMAP service seems snappy as ever.

this is the entry from cyrus.conf:

  lmtpunix   cmd="lmtpd" listen="/uio/PKG/config/var/imap/socket/lmtp" prefork=2

we are running several instances of Cyrus on each cluster node, and this
happens simultaneously to all instances on a given node.

looking at the code, it seems the wait happens inside
service/master.c:main, and probably is related to the lock file.  is it
possible there is a race condition?

any ideas are welcome!
-- 
Kjetil T.