Postgres 9.6.2 and pg_log

Good day all,

I just noticed an anomaly regarding the logging. I have my logging set up as follows:
log_filename = 'postgresql-%d.log'
log_truncate_on_rotation = on

My log file postgresql-21.log contains only entries for today (April 24). When I restart the service, entries correctly start accumulating in postgresql-24.log. For example, my postgresql-21.log contains:
2017-04-24 11:19:34 EDT LOG: received fast shutdown request
2017-04-24 11:19:34 EDT LOG: aborting any active transactions
2017-04-24 11:19:34 EDT LOG: autovacuum launcher shutting down
2017-04-24 11:19:35 EDT LOG: shutting down
2017-04-24 11:19:35 EDT LOG: database system is shut down

My postgresql-24.log contains:
2017-04-24 11:19:40 EDT LOG: database system was shut down at 2017-04-24 11:19:35 EDT
2017-04-24 11:19:40 EDT LOG: MultiXact member wraparound protections are now enabled
2017-04-24 11:19:40 EDT LOG: database system is ready to accept connections
2017-04-24 11:19:40 EDT LOG: autovacuum launcher started

This is on Windows 10, 64-bit
PostgreSQL 9.2.2, compiled by Visual C++ build 1800, 64-bit
(EnterpriseDB installer)

Note that this is not a major concern on my end; postgres 9.6.2 has otherwise been running flawlessly.

Mark Watson