Funny answers in mysql for IS NULL queries

Have you seen mysql returns non-NULL values for NULL query. If not you can try this out.
create table null_test(a int not null auto_increment, b int not null, primary key (a));
insert into null_test(a, b) values (0, 1); select * from null_test where a is null;

           | a | b |
        +---+---+
           | 1 | 1 |
           +---+---+
Then retry  mysql> select * from null_test where a is null;
Empty set (0.00 sec)
You can prevent this by 

• setting sql mode to NO_AUTO_VALUE_ON_ZERO. (Then next sequence number is generated only when NULL value for column is inserted.)

• And setting off SQL_AUTO_IS_NULL server variable. (When ON it returns last inserted row for a table that contains an AUTO_INCREMENT column.)

This behavior is useful for ODBC programs, such as Access. But when such mysql table is restored from a dump, data become different.