Thunderbird causes weird saslauthd auth failure

[Zoran Kikic]

Client: Thunderbird (V2 - beta 2) on Vista 32

I get a failure in my log when opening a (imap)mailbox with Tunderbird
but everything works!

#imap.conf
virtdomains: yes
defaultdomain: domain.xx
servername: domain.xx
loginrealms: domain.xx

saslauthd[55269] :cache_lookup    : [login=<myuser>] [service=] [realm=imap]: not found, update pending
#I did not define realm=imap anywhere...

saslauthd[55269] :cache_un_lock   : attempting to release lock on slot: 975
saslauthd[55269] :do_auth         : auth failure: [user=<..myuser..>] [service=imap] [realm=] [mech=pam] [reason=PAM auth error]
#[realm=] is now undefined??

Mulberry 4.0.8 (Win32) shows no errors. But when connecting with
Mulberry saslauthd even doesn't use cache. My log shows no 'cache_lookup', 'no do_auth'..
Does it mean no use of cache no error?!..

Well, is it a failure or not?