Wrong result from query that uses INTERSECT after UNION ALL

create table t1 (a int);

insert into t1 values (3), (1), (7), (3), (2), (7), (4);

create table t2 (a int);

insert into t2 values (4), (5), (9), (1), (8), (9);

create table t3 (a int);

insert into t3 values (8), (1), (8), (2), (3), (7), (2);

select * from t1 where a > 4

union all 

select * from t2 where a < 5

intersect

select * from t3 where a < 5

MariaDB [test]> select * from t1 where a > 4

    -> union all

    -> select * from t2 where a < 5

    -> intersect

    -> select * from t3 where a < 5

    -> ;

+------+

| a    |

+------+

|    7 |

|    1 |

+------+

2 rows in set

MariaDB [test]> select * from t2 where a < 5

    -> intersect

    -> select * from t3 where a < 5

    -> union all

    -> select * from t1 where a > 4;

+------+

| a    |

+------+

|    7 |

|    1 |

|    7 |

+------+

3 rows in set

MariaDB [test]> select version();

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

| version()             |

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

| 10.3.14-MariaDB-debug |

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

MariaDB [test]> select * from t1 where a > 4

    -> union all

    -> select * from t2 where a < 5

    -> intersect

    -> select * from t3 where a < 5;

+------+

| a    |

+------+

|    7 |

|    7 |

|    1 |

+------+

3 rows in set