MATCH() AGAINST( IN BOOLEAN MODE), results mismatch

drop table if exists t1;

CREATE TABLE t1 (

id INT UNSIGNED AUTO_INCREMENT NOT NULL PRIMARY KEY,

a VARCHAR(200),

b TEXT

) ENGINE = InnoDB STATS_PERSISTENT=0;

INSERT INTO t1 (a,b) VALUES

        ('MySQL Tutorial','DBMS stands for DataBase ...')  ,

        ('How To Use MySQL Well','After you went through a ...'),

        ('Optimizing MySQL','In this tutorial we will show ...');

ALTER TABLE t1 ADD FULLTEXT INDEX idx_1 (a);

ALTER TABLE t1 ADD FULLTEXT INDEX idx_2 (b);

SHOW CREATE TABLE t1;

START TRANSACTION;

INSERT INTO t1 (a,b) VALUES

        ('1001 MySQL Tricks','1. Never run mysqld as root. 2. ...'),

        ('MySQL vs. YourSQL','In the following database comparison ...'),

        ('MySQL Security','When configured properly, MySQL ...');

ROLLBACK;

select *, MATCH(a) AGAINST("Optimizing MySQL" IN BOOLEAN MODE) as x from t1;

MariaDB [test]> select *, MATCH(a) AGAINST("Optimizing MySQL" IN BOOLEAN MODE) as x from t1;

+----+-----------------------+-----------------------------------+----------------------------+

| id | a                     | b                                 | x                          |

+----+-----------------------+-----------------------------------+----------------------------+

|  1 | MySQL Tutorial        | DBMS stands for DataBase ...      | 0.000000001885928302414186 |

|  2 | How To Use MySQL Well | After you went through a ...      | 0.000000001885928302414186 |

|  3 | Optimizing MySQL      | In this tutorial we will show ... |        0.22764469683170319 |

+----+-----------------------+-----------------------------------+----------------------------+

3 rows in set (0.00 sec)

mysql> select *, MATCH(a) AGAINST("Optimizing MySQL" IN BOOLEAN MODE) as x from t1;

+----+-----------------------+-----------------------------------+--------------------+

| id | a                     | b                                 | x                  |

+----+-----------------------+-----------------------------------+--------------------+

|  1 | MySQL Tutorial        | DBMS stands for DataBase ...      | 0.0906190574169159 |

|  2 | How To Use MySQL Well | After you went through a ...      | 0.0906190574169159 |

|  3 | Optimizing MySQL      | In this tutorial we will show ... | 0.6961383819580078 |

+----+-----------------------+-----------------------------------+--------------------+

3 rows in set (0,00 sec)