Hello,

As written in my mail from yesterday, I took a close look this time.
It just happened to me again 10mins ago, while yesterday I kept connected during several hours without a logout or session kill.

Difference: Yesterday I was at home when I wrote the message, direct internet access. Now I'm at work behind a proxy. Maybe this fact changes the browser session behaviour.

Logs from my session:

SQL:
[25-Apr-2012 10:41:02 +0200]: query(1): SELECT vars, ip, changed FROM session WHERE sess_id = 'fq0m0vp31sqip858te5mnu1e67';
[25-Apr-2012 10:42:02 +0200]: query(1): SELECT vars, ip, changed FROM session WHERE sess_id = 'fq0m0vp31sqip858te5mnu1e67';
[25-Apr-2012 10:43:02 +0200]: query(1): SELECT vars, ip, changed FROM session WHERE sess_id = 'fq0m0vp31sqip858te5mnu1e67';
[25-Apr-2012 10:43:02 +0200]: query(1): UPDATE session SET changed='2012-04-25 10:43:02' WHERE sess_id='fq0m0vp31sqip858te5mnu1e67';
[25-Apr-2012 10:44:02 +0200]: query(1): SELECT vars, ip, changed FROM session WHERE sess_id = 'fq0m0vp31sqip858te5mnu1e67';
[25-Apr-2012 10:45:02 +0200]: query(1): SELECT vars, ip, changed FROM session WHERE sess_id = 'fq0m0vp31sqip858te5mnu1e67';
[25-Apr-2012 10:45:13 +0200]: query(1): SELECT vars, ip, changed FROM session WHERE sess_id = 'fq0m0vp31sqip858te5mnu1e67';
[25-Apr-2012 10:46:02 +0200]: query(1): SELECT vars, ip, changed FROM session WHERE sess_id = 'fq0m0vp31sqip858te5mnu1e67';
[25-Apr-2012 10:47:02 +0200]: query(1): SELECT vars, ip, changed FROM session WHERE sess_id = 'fq0m0vp31sqip858te5mnu1e67';
[25-Apr-2012 10:48:02 +0200]: query(1): SELECT vars, ip, changed FROM session WHERE sess_id = 'fq0m0vp31sqip858te5mnu1e67';
[25-Apr-2012 10:49:02 +0200]: query(1): SELECT vars, ip, changed FROM session WHERE sess_id = 'fq0m0vp31sqip858te5mnu1e67';
[25-Apr-2012 10:49:59 +0200]: query(1): DELETE FROM session WHERE sess_id = 'fq0m0vp31sqip858te5mnu1e67';
[25-Apr-2012 10:49:59 +0200]: query(1): INSERT INTO session (sess_id, vars, ip, created, changed) VALUES ('fq0m0vp31sqip858te5mnu1e67', 'bGFuZ3VhZ2V8czo1OiJlbl9VUyI7dGVtcHxiOjE7', 'xxx.xxx.xxx.xxx', '2012-04-25 10:49:59', '2012-04-25 10:49:59');
[25-Apr-2012 10:50:01 +0200]: query(1): SELECT vars, ip, changed FROM session WHERE sess_id = 'fq0m0vp31sqip858te5mnu1e67';
[25-Apr-2012 10:50:01 +0200]: query(1): UPDATE session SET vars='bGFuZ3VhZ2V8czo1OiJlbl9VUyI7dGVtcHxiOjE7dGFza3xzOjU6ImxvZ2luIjs=', changed='2012-04-25 10:50:01' WHERE sess_id='fq0m0vp31sqip858te5mnu1e67';
[25-Apr-2012 10:50:02 +0200]: query(1): DELETE FROM session WHERE sess_id = 'fq0m0vp31sqip858te5mnu1e67';
[25-Apr-2012 10:50:02 +0200]: query(1): INSERT INTO session (sess_id, vars, ip, created, changed) VALUES ('fq0m0vp31sqip858te5mnu1e67', 'bGFuZ3VhZ2V8czo1OiJlbl9VUyI7dGVtcHxiOjE7', 'xxx.xxx.xxx.xxx', '2012-04-25 10:50:02', '2012-04-25 10:50:02');
[25-Apr-2012 10:50:02 +0200]: query(1): DELETE FROM session WHERE sess_id = 'fq0m0vp31sqip858te5mnu1e67';
[25-Apr-2012 10:50:02 +0200]: query(1): INSERT INTO session (sess_id, vars, ip, created, changed) VALUES ('fq0m0vp31sqip858te5mnu1e67', 'bGFuZ3VhZ2V8czo1OiJlbl9VUyI7dGVtcHxiOjE7', 'xxx.xxx.xxx.xxx', '2012-04-25 10:50:02', '2012-04-25 10:50:02');

session log:
[25-Apr-2012 10:50:01 +0200]: Aborted session fq0m0vp31sqip858te5mnu1e67; no valid session data found

no entries in errors log.

http access log:
xxx.xxx.xxx.xxx - - [25/Apr/2012:10:41:02 +0200] "GET /?_task=mail&_action=check-recent&_mbox=INBOX&_list=1&_remote=1&_unlock=0&_=1335343261913 HTTP/1.1" 200 77
xxx.xxx.xxx.xxx - - [25/Apr/2012:10:42:02 +0200] "GET /?_task=mail&_action=check-recent&_mbox=INBOX&_list=1&_remote=1&_unlock=0&_=1335343321928 HTTP/1.1" 200 77
xxx.xxx.xxx.xxx - - [25/Apr/2012:10:43:02 +0200] "GET /?_task=mail&_action=check-recent&_mbox=INBOX&_list=1&_remote=1&_unlock=0&_=1335343382109 HTTP/1.1" 200 77
xxx.xxx.xxx.xxx - - [25/Apr/2012:10:44:02 +0200] "GET /?_task=mail&_action=check-recent&_mbox=INBOX&_list=1&_remote=1&_unlock=0&_=1335343441933 HTTP/1.1" 200 77
xxx.xxx.xxx.xxx - - [25/Apr/2012:10:45:02 +0200] "GET /?_task=mail&_action=check-recent&_mbox=INBOX&_list=1&_remote=1&_unlock=0&_=1335343501932 HTTP/1.1" 200 77
xxx.xxx.xxx.xxx - - [25/Apr/2012:10:46:02 +0200] "GET /?_task=mail&_action=check-recent&_mbox=INBOX&_list=1&_remote=1&_unlock=0&_=1335343561932 HTTP/1.1" 200 77
xxx.xxx.xxx.xxx - - [25/Apr/2012:10:47:02 +0200] "GET /?_task=mail&_action=check-recent&_mbox=INBOX&_list=1&_remote=1&_unlock=0&_=1335343621959 HTTP/1.1" 200 171
xxx.xxx.xxx.xxx - - [25/Apr/2012:10:48:02 +0200] "GET /?_task=mail&_action=check-recent&_mbox=INBOX&_list=1&_remote=1&_unlock=0&_=1335343681963 HTTP/1.1" 200 171
xxx.xxx.xxx.xxx - - [25/Apr/2012:10:49:02 +0200] "GET /?_task=mail&_action=check-recent&_mbox=INBOX&_list=1&_remote=1&_unlock=0&_=1335343741962 HTTP/1.1" 200 171
xxx.xxx.xxx.xxx - - [25/Apr/2012:10:50:01 +0200] "GET /?_task=mail HTTP/1.1" 200 8110
xxx.xxx.xxx.xxx - - [25/Apr/2012:10:50:01 +0200] "GET /skins/default/common.css?s=1330947632 HTTP/1.1" 304 -
xxx.xxx.xxx.xxx - - [25/Apr/2012:10:50:01 +0200] "GET /program/js/common.js?s=1331483103 HTTP/1.1" 304 -
xxx.xxx.xxx.xxx - - [25/Apr/2012:10:50:01 +0200] "GET /plugins/persistent_login/persistent_login.css?s=1321094906 HTTP/1.1" 304 -
xxx.xxx.xxx.xxx - - [25/Apr/2012:10:50:01 +0200] "GET /plugins/persistent_login/persistent_login.js?s=1321129484 HTTP/1.1" 304 -
xxx.xxx.xxx.xxx - - [25/Apr/2012:10:50:01 +0200] "GET /program/js/jquery.min.js?s=1315898178 HTTP/1.1" 304 -
xxx.xxx.xxx.xxx - - [25/Apr/2012:10:50:01 +0200] "GET /program/js/app.js?s=1331483100 HTTP/1.1" 304 -


Again, as mentioned yesterday, the session was DELETEd and then immediately reinserted in the session table. But why?

Thiago, are you/your users also using a proxy by any chance?