"Index for table .. is corrupt; try to repair it" in error log after failed attempt to add index on persistent column

CREATE TABLE t1 ( 

  pk BIGINT AUTO_INCREMENT,

  f1 CHAR(15),

  f2 INT,

  v1 CHAR(10) AS (f1) VIRTUAL,

  v2 INT AS (f2) PERSISTENT,

  PRIMARY KEY(pk)

) ENGINE=MyISAM;

SET SQL_MODE= 'STRICT_TRANS_TABLES';

INSERT INTO t1 (f1,f2) VALUES

  ('0001',1),('01000100',7),('00011',9),('110100011100',1),

  (NULL,76),('000100101',1),('011011111',0),('01010',3),

  ('001001111',8),('01110',4),('0110000011000',1),('101110001110100',4),

  ('0101100',5),('0000010001110',1),('101111011100000',9),('00',0),

  ('1101000100100',6),(NULL,0),('0',8),('1',8),

  ('0',1),('001011100',6),('0111',93),('00001000110111',0),('11110',6),

  ('111000010',4),('10101101101110',5),('10',5),('00011101001',29),

  ('1',8),('111001',9),('01111',2),('100011011111100',4),

  ('1100',8),('101011011110110',1),('10010100101',4),(NULL,244),

  (NULL,1),('0100',109),('11000',8),('0000111',5),

  ('1111100000',9),('0010001',9),('01111111000000',1),('011100100',5),

  ('100101',2),('0',6),('01000001101101',9),('001110000101',3),

  ('1001',0),('10011101000110',0),(NULL,4),('00',8),

  ('01',1),('1',5),('101111101011',1),('1010111010',110),

  ('11010001001',9),(NULL,8),('11110111',1),('0',8),

  ('1111',2),(NULL,71),('11000101',9),('0111111011',61),

  ('0',6),('10110011',0),('101010',7),(NULL,7),

  ('00111',7),('0',35),('10000101',7),(NULL,9),

  ('000000001010',0),(NULL,2),('10111101000',1),(NULL,6),

  ('0101000010101',5),('01111000100010',5),('0',3),('01100',2),

  (NULL,6),('0011110',9),('010011',17),('1001',2),

  ('01010000110',1),('011000',8),(NULL,9),('010000011',2),

  ('111110100100000',8),('10000',0),('0000111110',9),('1101111',4),

  ('010110',23),('00110',4),('1',1),('011000110',0),

  ('101110',8),('0001010111100',1),('011101',6);

--error 0,ER_DATA_TOO_LONG

ALTER TABLE t1 ADD KEY (v2);

# Cleanup

DROP TABLE t1;

2018-12-22 17:26:35 139905558898432 [ERROR] mysqld: Index for table './test/#sql-1730_4.MYI' is corrupt; try to repair it

^ Found warnings in /data/bld/10.2/mysql-test/var/log/mysqld.1.err