pseudo_slave_mode variable inconsistent behavior

SELECT @@pseudo_slave_mode;

--error ER_BASE64_DECODE_ERROR

BINLOG ' a';

SELECT @@pseudo_slave_mode;

SHOW SESSION VARIABLES LIKE '%pseudo_slave_mode%';

SET pseudo_slave_mode=1;

SHOW WARNINGS;

12.2.0-dbg>SELECT @@pseudo_slave_mode;

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

| @@pseudo_slave_mode |

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

|                   0 |

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

1 row in set (0.000 sec)

12.2.0-dbg>BINLOG ' a';

ERROR 1575 (HY000): Decoding of base64 string failed

12.2.0-dbg>SELECT @@pseudo_slave_mode;

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

| @@pseudo_slave_mode |

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

|                   0 |

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

1 row in set (0.000 sec)

12.2.0-dbg>SHOW SESSION VARIABLES LIKE '%pseudo_slave_mode%';

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

| Variable_name     | Value |

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

| pseudo_slave_mode | OFF   |

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

1 row in set (0.003 sec)

12.2.0-dbg>SET pseudo_slave_mode=1;

Query OK, 0 rows affected, 1 warning (0.001 sec)

12.2.0-dbg>SHOW WARNINGS;

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

| Level   | Code | Message                            |

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

| Warning | 1231 | 'pseudo_slave_mode' is already ON. |

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

1 row in set (0.000 sec)