Description of problem:
I am using Scientific Linux 6.1 (a free Red Hat Enterprise Linux derivative).
I used openldap-2.4.19-15.el6_0.2.x86_64 since July 2011 without any problem. Since the upgrade to openldap-2.4.23-15.el6.x86_64 applied on 18 January 2012, we are experimenting unexpected slapd server crashes. Nothing is written in the 
log, no core is created. Tried to solve installing openldap-2.4.23-15.el6_1.3.x86_64 (from fastbugs repository), but it crashed too.


Version-Release number of selected component (if applicable):
2.4.23-15.el6.x86_64
2.4.23-15.el6_1.3.x86_64


How reproducible:
Not really reproducible, but on a cloned server containing the same users database, I run 20 processes running the following script until slapd crashed (it took about 2 hours).

#!/bin/bash

for ((;1==1;))
do
  ldapsearch -x -v  -h ldap1core.icgeb.org "uid=palmi"> /dev/null 2>&1
  ldapsearch -x -v  -h ldap1core.icgeb.org "uid=palmi" -ZZ > /dev/null 2>&1
  ldapsearch -x -v  -h ldap1core.icgeb.org "mail=Dario.Palmisano" -ZZ > /dev/null 2>&1
done


Steps to Reproduce:
1.
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Actual results:
After a couple of hours slapd exited (crashed) without any message in /var/log/ldap.log (slapd.conf had loglevel 256) or /var/log/messages.

Expected results:
slapd should continue working

Additional info: