log_min_messages=debug5, despite an explicit setting to warning on postgresql.conf

We ran into a production issue during our maintenance window when I switched over LifeKeeper/PostgreSQL nodes from one to another. We noticed that the database was 1000 times slower than it usually is, then realized that the log_min_messages setting was set to 'debug5' for no reason.

Facts:
The postgresql.conf file has always been using the default value, which is 'warning'.An attempt to explicitly set log_min_messages=warning and reload could not override the setting of 'debug5'.The heavy debug5 logging on our production system drastically slowed down our database, and eventually filled up the root file system (due to the huge /var/log/postgresql)The LifeKeeper failover has been done in a recent past with the same unmodified postgresql.log file without such an excessive logging behavior.Changing log_destination from syslog to stderr appeared to have done the trick, after hours of troubleshooting. The log_min_messages value took the explicit setting from postgresql.log ('warning') and restored our database performance.
I could not find any relevant issue reported and want to see if anyone has a clue about this issue.

Thank you,
-Kong