Unknown in place of application name

Hi All

I have enabled logging parameters in PostgreSQL 9.6.

log_line_prefix = %t %a

log_connection = on

log_disconnection = on

After enabling I have checked the log and found that all new connections are showing unknown for application name however it is showing application name in disconnection. Same is tested with multiple applications and getting same result.

2017-08-07 18:55:44 IST [[unknown]] LOG: connection received: host=[local]
2017-08-07 18:55:48 IST [[unknown]] LOG: connection received: host=[local]
2017-08-07 18:55:48 IST [[unknown]] LOG: connection authorized: user=postgres database=postgres
2017-08-07 18:55:54 IST [psql.bin] LOG: disconnection: session time: 0:00:06.004 user=postgres database=postgres host=[local]

Kindly suggest.

Thanks and Regards:
Amandeep Singh