Proxy backends use ldap_set_option(3) to set alias dereferencing
requested by a search operation (and do not clean it up afterwards, as
far as I can tell). Since LDAP handlers are pooled and reused, this
behavior is inherently broken.
I note you committed this with an ldap_int_* interface. But it could
be useful outside OpenLDAP code too.
Seems to me this is what client-side controls are for. Extending the
client-side functionality without needing a new API.