[exim] LDAP connection caching problem?

Exim 4.50, 4.52:
routing seems to work OK, but the delivery process (in some cases) can't seem to
talk to LDAP. The search should return no results. OpenLDAP 2.0.x library,
Novell eDirectory 8.7.3.4 server.

exim -d -M ... yields:

after ldap_url_parse: host=... port=636
re-using cached connection to LDAP server ...:636
Start search
search ended by ldap_result yielding -1
ldap_result failed
ldap_result failed: 81, Can't contact LDAP server
lookup deferred: ldap_result failed: 81, Can't contact LDAP server
condition check lookup defer

Any thoughts?
TIA,
John