Inconsistent behaviors when casting into time

DROP TABLE t1;

CREATE TABLE t1 (c1 CHAR(20));

INSERT INTO t1 VALUES (9430886);

SELECT (CAST(c1 AS TIME)) FROM t1; -- {NULL}

DROP TABLE t1;

CREATE TABLE t1 (c1 MEDIUMINT UNSIGNED);

INSERT INTO t1 VALUES (9430886);

SELECT (CAST(c1 AS TIME)) FROM t1; -- actual: {838:59:59}, expected: {null}