BUG #7528: Spurious empty log file created

The following bug has been logged on the website:

Bug reference: 7528
Logged by: Alexander Jerusalem
Email address: ajeru(at)topolyte(dot)com
PostgreSQL version: 9.2.0
Operating system: Linux (Ubuntu x86_64, kernel version 2.6.18)
Description:

I have the following log configuration in postgresql.conf:

log_destination = 'csvlog'
logging_collector = on
log_directory = 'pg_log'
log_filename = 'pg-%Y-%m-%d_%H%M%S.log'
log_rotation_age = 1d
log_rotation_size = 10MB

After removing all files from pg_log and relaunching the postgres server,
pg_log contains two files instead of one: pg-xxx.log and pg-xxx.csv.
According to the documentation, only pg-xxx.csv should exist. And in fact
only pg-xxx.csv is actually written to whilst pg-xxx.log remains empty.

Using a .csv extenson or no extension at all for the log_filename setting
doesn't help either. Postgres always creates a file named exactly as the
log_filename setting says and a second one with .csv appended.