Hm, what does this question have to do with OpenLDAP software?
ldapsearch knows nothing about DNS or Kerberos. The behavior you're seeing is Kerberos-specific, and has nothing to do with LDAP or OpenLDAP software.
You are right. With simple bind (-x) ldapsearch does not do any of the reverse lookups. The behavior I've described probably comes from SASL.
Thanks -- Zaar