custom log. variable %h reports [unknown]

og_connections = on

log_disconnections = on

log_line_prefix = '===========> %h %u %t %p %x: [%l-1]'    

log_hostname = off

But in logs i see:

===========>  [unknown] 2016-01-26 17:07:46 UTC 1664 0: [1-1]LOG:  connection received: host=192.168.112.181 port=50321

===========> 192.168.112.181 postgres 2016-01-26 17:07:46 UTC 1664 0: [2-1]LOG:  connection authorized: user=postgres database=lb_upr

===========>  [unknown] 2016-01-26 17:08:27 UTC 1665 0: [1-1]LOG:  connection received: host=192.168.112.181 port=50330

The off. docs says that variable %h stands for Remote hostname or IP.

Any ideas?

PS 

DNS server configured to NOT answer on r-lookup queries, because he does not have reverse zone for  my network.