mysql access denied for only one IP on a multi-NIC system

mysql access denied for only one IP on a multi-NIC system

I'm having this strange problem. We have a ubuntu 12.04 server with 2
NICs. One public with 172.30.1.1, the other is private with 192.168.1.1.
We have a MySQL server running. In /etc/mysql/my.conf, we have
bind-address = 0.0.0.0.
A table is created and privilege granted.
CREATE DATABASE db;
GRANT ALL ON db.* TO 'user0'@'%' IDENTIFIED BY 'password';
GRANT ALL ON db.* TO 'user0'@'localhost' IDENTIFIED BY 'password';
The hostname is 'myhost', and it's in /etc/hostname. /etc/hosts has
127.0.0.1 localhost
127.0.1.1 myhost
192.168.1.1 myhost
When I connect with 172.30.1.1, it's fine. But when I use 192.168.1.1, the
access is denied. mysql -h 192.168.1.1 -uuser0 -ppassword ERROR 1045
(28000): Access denied for user 'user0'@'myhost' (using password: YES) I
have the user table like this.
mysql> SELECT user, host FROM mysql.user;
+------------------+-----------+
| user | host |
+------------------+-----------+
| user0 | % |
| root | 127.0.0.1 |
| root | ::1 |
| | localhost |
| debian-sys-maint | localhost |
| user0 | localhost |
| root | localhost |
| | myhost |
| root | myhost |
+------------------+-----------+
I observed the difference is that I have 192.168.1.1 myhost line in
/etc/hosts file; not 172.30.1.1. If I remove that line or change the
hostname after the IP, it will work fine. If I add 172.30.1.1 myhost to
/etc/hosts, then I can't connect with 172 IP. How to explain this?