Wrong result (extra rows) with an index on a VIRTUAL column

CREATE TABLE t1 (

  pk INT(11) NOT NULL,

  c VARCHAR(3) DEFAULT NULL,

  vc VARCHAR(3) GENERATED ALWAYS AS (c) VIRTUAL,

  PRIMARY KEY (pk),

  KEY (vc)

) ENGINE=InnoDB;

INSERT INTO t1 (pk,c) VALUES 

(1,'foo'),(2,'bar'),(3,'qux'),(4,'foo'),(5,'bar'),

(6,'qux'),(7,'foo'),(8,'bar'),(9,'qux'),(10,'foo');

CREATE TABLE t2 (

  pk INT(11) NOT NULL,

  c VARCHAR(3),

  PRIMARY KEY (pk)

) ENGINE=InnoDB;

INSERT INTO t2 VALUES (1,'foo'),(2,'bar');

SELECT t1.pk, t2.pk FROM t1, t2 WHERE t2.c = t1.vc AND t2.c = t1.c AND t2.pk > t1.pk;

+----+----+

| pk | pk |

+----+----+

|  1 |  1 |

|  4 |  1 |

|  7 |  1 |

| 10 |  1 |

|  2 |  2 |

|  5 |  2 |

|  8 |  2 |

+----+----+

7 rows in set (0.00 sec)