2.4.21 and 2.4.22 exit on signal 6

Hi list,
  I'm experiencing some problems with and LDAP box which used to run
  2.4.21 and has been upgraded to 2.4.22

The box act as a pam_ldap/nsswitch login server for a bunch of boxes,
let's say 20, and serve the mail server and web proxy server as a
user base.

The box has 2G of RAM and has an average load very low, let's say
top/systat shows 0.40.

The issue is that it happens from time to time every 2/4 days that the
slapd daemon exits on signal 6:

May 12 01:00:00 polido kernel: pid 27153 (slapd), uid 389: exited on
signal 6

Then i restart the process everything looks fine and no corruption
seems to happen in the DB. The box is a FreeBSD 8

Any clue is really appreciated.

Thanks
-- 
Massimo Lusetti