nssov works fine, unable to set nssov-pam-session

Before enabling nssov I have got nslcd working, so the transition from one to another was clear (ubuntu 12.04.1, openldap 2.4.28-1.1ubuntu4.2).

according to slapo-nssov man page I have added to my slapd.conf:

moduleload nssov overlay nssov nssov-pam userhost nssov-pam-session login nssov-pam-session sshd

but olcOverlay=nssov,olcDatabase=hdb,cn=config has no olcNssPamSession and its related values after creation of db.

When I add olcNssPamSession into cn=config with above values by hand - loginstatus is working well, but when nssov-pam-session into slapd.conf - none.

Does it mean that I am missed something to correctly set nssov-pam-session in slapd.conf?