duplicated naming context when using syncrepl proxy

[Jochen Keutel <mlists@keutel.de>]

Hallo,
  I'm using OpenLDAP on Debian 9 (2.4.44) and started to configure 
replication: szenario syncrepl proxy (push based replication, see 18.3.5 
in OpenLDAP Admin Guide - "primary directory also contains back-ldap 
databases"). Configuring the LDAP backend leads unfortunately to a root 
DSE showing the same name context twice:

namingContexts: dc=keutel,dc=de
namingContexts: dc=keutel,dc=de

Is this a known problem? Esp. this stops PHPLDAPAdmin from working: It 
prints a lot of PHP arrays in this case.
I've set "hidden on" for this backend but the problem remains.

My configuration:

1. slapd.conf on server1 (master):

database ldap
hidden on
suffix          "dc=keutel,dc=de"
rootdn          "cn=admin,dc=keutel,dc=de"
uri ldaps://server2/

lastmod on
restrict all

acl-bind    bindmethod=simple
        binddn="cn=replication,dc=keutel,dc=de"
        credentials=secret

syncrepl    rid=001
        provider=ldaps://server1/
        binddn="cn=replication,dc=keutel,dc=de"
        bindmethod=simple
        credentials=secret
        searchbase="dc=keutel,dc=de"
        type=refreshAndPersist
        retry="5 5 300 5"

2. converting this to dynamic config using slaptest gives the following 
entry:

dn: olcDatabase={2}ldap
objectClass: olcDatabaseConfig
objectClass: olcLDAPConfig
olcDatabase: {2}ldap
olcHidden: TRUE
olcSuffix: dc=keutel,dc=de
...

3. starting slapd with this dynamic configuration

4. reading rootDSE: attribute namingContexts occurs twice with the same 
value.

How can this be solved?

Regards
Jochen.