Further info: slapd.1.log has entries like this:
bdb_search: 15 does not match filter bdb_search: 16 does not match filter bdb_search: 17 does not match filter bdb_search: 18 does not match filter send_ldap_result: conn=293 op=1 p=3 send_ldap_result: err=0 matched="" text="" send_ldap_response: msgid=2 tag=101 err=0 ber_flush2: 154 bytes to sd 15 conn=293 op=1 SEARCH RESULT tag=101 err=0 nentries=0 text= connection_get(15) connection_get(15): got connid=293 connection_read(15): checking for input on id=293 ber_get_next ber_get_next: tag 0x30 len 5 contents: ber_get_next ber_get_next on fd 15 failed errno=0 (Undefined error: 0) connection_closing: readying conn=293 sd=15 for close connection_close: deferring conn=293 sd=15 conn=293 op=2 do_unbind conn=293 op=2 UNBIND connection_resched: attempting closing conn=293 sd=15 connection_close: conn=293 sd=15 conn=293 fd=15 closed
Note the error...