ALTER TABLE silently ignores AS ROW attribute

create or replace table t1 (i int);

alter table t1 add r timestamp(6) generated always as row start;

show create table t1 \G

       Table: t1

Create Table: CREATE TABLE `t1` (

  `i` int(11) DEFAULT NULL,

  `r` timestamp(6) NOT NULL DEFAULT '0000-00-00 00:00:00.000000'

) ENGINE=InnoDB DEFAULT CHARSET=latin1

1 row in set (0.00 sec)

MariaDB [test]> create or replace table t1 (i int, r timestamp(6) generated always as row start);

ERROR 4123 (HY000): Wrong parameters for `t1`: missing 'WITH SYSTEM VERSIONING'