RoundCube perfomance bug with contacts above 1000 in MySQL

[rc-user]

Huge delays at user's login to RoundCube. If user has about of 2000 messages in the mailbox, the delay is 2-3 minutes. Generally 435 records in table "users", 1400 in table "contacts", 333 in "contactgroupmembers", 56 in "contactgroups".

Switching RoundCube sql queries logging on shows delay at «UPDATE session SET» query:

[08-Feb-2012 16:05:10 +0000]: query(1): SELECT cache_id, data, cache_key FROM cache WHERE user_id = 84 AND cache_key = 'IMAP.messagecount' ORDER BY created DESC LIMIT 0, 1;
[08-Feb-2012 16:05:10 +0000]: query(1): UPDATE cache SET created = now(), data = 'a:5:{s:5:\"INBOX\";a:2:{s:3:\"ALL\";i:4041;s:6:\"UNSEEN\";i:1924;}s:6:\"Drafts\";a:1:{s:6:\"UNSEEN\";i:0;}s:4:\"Sent\";a:1:{s:6:\"UNSEEN\";i:0;}s:4:\"Junk\";a:1:{s:6:\"UNSEEN\";i:0;}s:5:\"Trash\";a:1:{s:6:\
"UNSEEN\";i:0;}}' WHERE user_id = 84 AND cache_key = 'IMAP.messagecount';
[08-Feb-2012 16:05:10 +0000]: query(1): UPDATE session SET vars='bGFuZ3VhZ2V8czo1OiJydV9SVSI7aW1
<-- TRUNCATED -->
5MjQ7czo2OiJEcmFmdHMiO2k6MDtzOjQ6IlNlbnQiO2k6MDtzOjQ6Ikp1bmsiO2k6MDtzOjU6IlRyYXNoIjtpOjA7fQ==',changed='2012-02-08 16:05:10' WHERE sess_id='61eh0naumln6odsn9pvg8mdki4';
[08-Feb-2012 16:06:29 +0000]: query(1): UPDATE cache SET created = now(), data = 'a:1:{s:5:\"INBOX\";a:2:{s:3:\"ALL\";i:4141;s:6:\"UNSEEN\";i:1924;}}' WHERE user_id = 84 AND cache_key = 'IMAP.messagecount';
[08-Feb-2012 16:06:29 +0000]: query(1): SELECT vars, ip, changed FROM session WHERE sess_id = '6
1eh0naumln6odsn9pvg8mdki4';

Also there are no delays after completely cleaning table «contacts».

All RoundCube settings are defaults. IMAP server on the same host. RoundCube version 0.7.1 (latest). MySQL — 5.1.61 PHP (php-fpm) — 5.3.8 Nginx -1.1.13

Is it possible to fix this RoundCube perfomance bug with contacts above 1000 ?