Pls help:delete missing in multi-master environment

["ST Wong (ITSC)" <ST@itsc.cuhk.edu.hk>]

Hi all,
 
I set up a 2 server multi-master environment using OpenLDAP 2.4.9 + BerkeleyDB 4.6 on CentOS 5.1.  Make test and simple load test on add/mod/del are okay.  However, seems some records are not replicated in delete phrase when there are lot of simultaneous delete operations (e.g. 10 threads spawned from 2 clients to add/del 100 users in each threads).   I'm newbie to syncrepl and have no idea about the problem are scanning debug output.  My slapd.conf syncrepl section follows:
 
#master
overlay syncprov
syncprov-checkpoint 100 10
syncprov-sessionlog 100

#consumer
syncrepl rid=001
        provider=ldaps://192.168.28.69
        starttls=yes
        tls_reqcert=never
        tls_cacert=/etc/CA/cacert.pem
        type=refreshAndPersist
        retry="5 + 5 +"
        searchbase="dc=mydomain,dc=hk"
        schemachecking=off
        bindmethod=simple
        binddn="cn=replicator,ou=People,dc=mydomain,dc=edu"
        credentials=secret

Would anyone pls help?   Sorry for the newbie question.
 
Thanks a lot.
/st wong