Copying from INT/DOUBLE to ENUM is inconsistent

DROP TABLE IF EXISTS t1,t2;

CREATE TABLE t1 (a ENUM('9e200','9e100'));

CREATE TABLE t2 (a DOUBLE);

INSERT INTO t2 VALUES ('9e100');

INSERT INTO t1 SELECT * FROM t2;

SELECT * FROM t1;

+------+

| a    |

+------+

|      |

+------+

DROP TABLE IF EXISTS t1;

CREATE TABLE t1 (a DOUBLE);

INSERT INTO t1 VALUES (9e100);

ALTER TABLE t1 MODIFY a ENUM('9e200','9e100');

SELECT *FROM t1;

+-------+

| a     |

+-------+

| 9e100 |

+-------+