FULLTEXT index disables foreign-key enforcement while metadata still reports the constraint

DROP DATABASE IF EXISTS test_fkft;

CREATE DATABASE test_fkft;

USE test_fkft;

CREATE TABLE parent (

  c0 varchar(16) NOT NULL,

  PRIMARY KEY (c0)

) ENGINE=InnoDB;

CREATE TABLE child (

  id int NOT NULL,

  c0 varchar(16) DEFAULT NULL,

  PRIMARY KEY (id),

  CONSTRAINT fk0 FOREIGN KEY (c0) REFERENCES parent (c0)

) ENGINE=InnoDB;

INSERT INTO parent (c0) VALUES ('a');

INSERT INTO child (id, c0) VALUES (1, 'a');

CREATE FULLTEXT INDEX ft ON child (c0);

-- Must fail with a foreign-key error. MariaDB accepts it.

-- MySQL fails with "Cannot add or update a child row: a foreign key constraint fails (`test_fkft`.`child`, CONSTRAINT `fk0` FOREIGN KEY (`c0`) REFERENCES `parent` (`c0`))"

UPDATE child SET c0 = 'b';

-- Catalog still claims fk0. Expected: no such row, or SHOW without CONSTRAINT.

SELECT TABLE_NAME, CONSTRAINT_NAME, COLUMN_NAME,

       REFERENCED_TABLE_NAME, REFERENCED_COLUMN_NAME

FROM information_schema.KEY_COLUMN_USAGE

WHERE TABLE_SCHEMA = 'test_fkft'

  AND REFERENCED_TABLE_NAME IS NOT NULL;

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

| TABLE_NAME | CONSTRAINT_NAME | COLUMN_NAME | REFERENCED_TABLE_NAME | REFERENCED_COLUMN_NAME |

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

| child      | fk0             | c0          | parent                | c0                     |

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

-- Violation of foreign key constraints

SELECT child.c0 

FROM child 

WHERE NOT EXISTS (SELECT 1 FROM parent WHERE parent.c0 = child.c0);

+------+

| c0   |

+------+

| b    |

+------+