System variable change not recorded in context

CREATE TABLE t1 (a int);

set sql_notes=0;

set optimizer_record_context=ON;

EXPLAIN SELECT * FROM t1;

SELECT context INTO DUMPFILE 'context1.txt' FROM INFORMATION_SCHEMA.OPTIMIZER_CONTEXT;

source context1.txt;

MariaDB [m8]> explain extended select * from t1;

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

| id   | select_type | table | type | possible_keys | key  | key_len | ref  | rows | filtered | Extra |

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

|    1 | SIMPLE      | t1    | ALL  | NULL          | NULL | NULL    | NULL | 1    |   100.00 |       |

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

1 row in set (0.001 sec)

MariaDB [m8]> explain extended select * from t1;

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

| id   | select_type | table | type | possible_keys | key  | key_len | ref  | rows | filtered | Extra |

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

|    1 | SIMPLE      | t1    | ALL  | NULL          | NULL | NULL    | NULL | 1    |   100.00 |       |

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

1 row in set, 1 warning (0.001 sec)

MariaDB [m8]> show warnings;

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

| Level | Code | Message                                    |

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

| Note  | 1003 | select `m8`.`t1`.`a` AS `a` from `m8`.`t1` |

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

1 row in set (0.001 sec)