Session on Database being lost

[eluser]Paulodemoc[/eluser]
Hello guys, I am having trouble using CI's Session for some reason. I started using database sessions, it solved a lot of my problems. But now, something odd seems to be happening. If I put the session to expire after 10 seconds, then it works fine, after 10 seconds I have to login again. But if I put it to expire after 7200 (2 hours), sometimes it expires after 2 hours, sometimes after 40 minutes of idleness, sometimes after 10... Anyone know what might be causing this?

This is my session config on the config file:

Code:

$config['sess_cookie_name'] = 'ccm_session';
$config['sess_expiration'] = 7200;
$config['sess_encrypt_cookie'] = FALSE;
$config['sess_use_database'] = TRUE;
$config['sess_table_name'] = 'ci_sessions';
$config['sess_match_ip'] = TRUE;
$config['sess_match_useragent'] = TRUE;
$config['sess_time_to_update'] = 300;