sftp-internal doesn't use specified log facility

Hi,
I'm trying to configure logging for SFTP activity of our users on our production server. We are not using chroot.
I have 2 RedHat servers: 5.10 (test server) and 5.6 (production).

The versions are outdated, I'll update them as soon as I can (I know I have to do this). However, it is not done yet :(

The thing is that I've configured logging for SFTP activity on our test server (RH 5.10), using following subsystem in /etc/ssh/sshd_config :
Subsystem sftp /usr/libexec/openssh/sftp-server -l INFO -f LOCAL3
and in /etc/syslog.conf:
local3.* /var/log/sftp/sftp.log

I have history of SFTP sessions in /var/log/sftp/sftp.log now on the test server.
I've configured the same settings on our production server, restarted ssh, but nothing sowed up in the log.

Syslog work, as execution of the following command:
echo test | logger -it logger_test -p local3.notice
adds a message in the /var/log/sftp/sftp.log.

Quesion: What could be a reason?
Will upgrade of production server to 5.11 help to solve the problem?

Thanks!