REFERENTIAL_CONSTRAINTS.UNIQUE_CONSTRAINT_NAME incorrectly reports a non-unique index

CREATE TABLE parent (c0 INT, c1 INT, PRIMARY KEY (c0));

CREATE TABLE child (c0 INT, c1 INT, PRIMARY KEY (c0));

INSERT INTO parent VALUES (1, 1), (2, 2);

INSERT INTO child VALUES (1, 1);

ALTER TABLE parent ADD INDEX i0 (c1);

ALTER TABLE parent ADD UNIQUE KEY uk0 (c1);

ALTER TABLE child

ADD CONSTRAINT fk0 FOREIGN KEY (c1) REFERENCES parent (c1);

SELECT CONSTRAINT_NAME, UNIQUE_CONSTRAINT_NAME

FROM information_schema.REFERENTIAL_CONSTRAINTS

WHERE CONSTRAINT_SCHEMA = DATABASE()

  AND CONSTRAINT_NAME = 'fk0';

CONSTRAINT_NAME | UNIQUE_CONSTRAINT_NAME

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

fk0             | i0

SELECT CONSTRAINT_NAME, CONSTRAINT_TYPE

FROM information_schema.TABLE_CONSTRAINTS

WHERE TABLE_SCHEMA = DATABASE()

  AND TABLE_NAME = 'parent';

PRIMARY | PRIMARY KEY

uk0     | UNIQUE

fk0 | uk0