log_min_duration_statement setting is ignored

Question

I am running Postgresql 9.1 on Ubuntu. Exact Postgresql version is 9.1+129ubuntu1 as my package manager shows.

I have 2 databases that are actively in use and they are used from a remote server.

I wish to log queries that have a long execution time. So I set following parameters in /etc/postgresql/9.1/main/postgresql.conf file

log_min_duration_statement = 10000
log_statement = 'mod'

so Postgresql will log queries that takes longer than 10 seconds.

But when I reload the postgres configuration, Postgresql begins to log every query that fits log_statement value. That I set duration to 100 seconds to be sure

log_min_duration_statement = 100000

But Postgresql keep logging every query that fits log_statement value, regardless of log_min_duration_statement value.

Setting log_statement to none seemed to stop logging.

Is there something that I missed about the configuration?