Mailbox of different user is shown when logged twice as different user from same host

have squirrenmail 1.4.13 configured on FC8 with sendmail,procmail as
delivery agent, dovecot(imap) ,Using MAILDIR, enabled secure_login
plugin, and using password/shadow and system user .

When I
login through squirrelmail every thing works fine . But when I login
again from the same host as a different user with new browser
session, the mailbox of the new user displays correctly but the
first user session displays the inbox of the second user . ie if I
have two https sessions from a single machine and login as two
different users the inbox of the later user is displayed in both the
sessions.

I checked the logs of dovecot and the following is noticed

dovecot:
May 06 11:12:25 Info: imap-login: Login: user=<ath>,
method=PLAIN, rip=::ffff:127.0.0.1, lip=::ffff:127.0.0.1, secured
dovecot: May 06 11:12:25 Info: IMAP(ath): Disconnected: Logged out

there
are lots of messages for a single login . Also the USER shown above
is the user of the second session and is displayed when i try to access
the first htts session



dovecot -n (reports the following)

# 1.0.5: /etc/dovecot.conf
log_path: /var/log/dovecot
protocols: imap imaps
ssl_disable: yes
login_dir: /var/run/dovecot/login
login_executable: /usr/libexec/dovecot/imap-login
mail_location: maildir:~/Maildir
auth default:
passdb:
driver: pam
userdb:
driver: passwd


kindly help