JSON_ARRAYAGG result differs when using HAVING or not

CREATE TABLE tst (a INTEGER, b VARCHAR(255));

INSERT INTO tst VALUES (1, 'test string');

SELECT a, JSON_ARRAYAGG(b) AS js FROM tst GROUP BY 1;

/* Correct:

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

| a    | js              |

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

|    1 | ["test string"] |

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

*/

SELECT a, JSON_ARRAYAGG(b) AS js FROM tst GROUP BY 1 HAVING a=1;

/* Correct:

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

| a    | js              |

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

|    1 | ["test string"] |

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

*/

SELECT  a, JSON_ARRAYAGG(b) AS js FROM tst GROUP BY 1 HAVING js<>'';

/* Extra brackets:

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

| a    | js                |

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

|    1 | [["test string"]] |

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

*/

-- but at the same time it has correct value within HAVING conditions:

SELECT  a, JSON_ARRAYAGG(b) AS js FROM tst GROUP BY 1 HAVING js='["test string"]';

/*

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

| a    | js                |

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

|    1 | [["test string"]] |

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

*/

SELECT  a, JSON_ARRAYAGG(b) AS js FROM tst GROUP BY 1 HAVING js='["test string"]';

/*

Empty set (0,002 sec)

*/