[Dovecot] Strange behavior of mysql 4.1.8/9 + dovecot 1.0-test58~test61 on Fedora 3 x86_64 machine

[#LIU QI#]

I've built & configured the dovecot to use mysql as the passdb and
userdb. However, dovecot-auth always claims that the username/password
of mysql server is wrong (access denied by mysql server) during the
connection. When I set the password to NULL, it can successfully connect
to mysql server! I am 100% sure that I typed the correct password (by
copy & paste), and I can successfully use this username/password connect
to mysql server by mysqladmin and other mysql clients. I even wrote a C
program which also successfully connects to mysql server. Furthermore,
even I want to use pam_mysql in dovecot, the pam library also claims
that it cannot connect to mysql server, but pam_mysql can be
successfully used in postfix (exactly the same pam configuration, the
same database, the same table, and the same username/password).

Can anybody give me a hint why? Thank you very very very very much....
Crying for help....