CONSTRAINT `time_period` failed for `sbtest`.`sbtest1` unclear error while adding time_period

MariaDB [sbtest]> alter table sbtest1 add column time_1 timestamp(6);

Query OK, 0 rows affected (0.046 sec)

Records: 0  Duplicates: 0  Warnings: 0

MariaDB [sbtest]> alter table sbtest1 add column time_2 timestamp(6);

Query OK, 0 rows affected (0.041 sec)

Records: 0  Duplicates: 0  Warnings: 0

MariaDB [sbtest]> show create table sbtest1\G

*************************** 1. row ***************************

       Table: sbtest1

Create Table: CREATE TABLE `sbtest1` (

  `id` int(11) NOT NULL AUTO_INCREMENT,

  `k` int(11) NOT NULL DEFAULT 0,

  `c` char(120) NOT NULL DEFAULT '',

  `pad` char(60) NOT NULL DEFAULT '',

  `time_1` timestamp(6) NOT NULL DEFAULT '0000-00-00 00:00:00.000000',

  `time_2` timestamp(6) NOT NULL DEFAULT '0000-00-00 00:00:00.000000',

  PRIMARY KEY (`id`),

  KEY `k_1` (`k`)

) ENGINE=InnoDB AUTO_INCREMENT=220753785 DEFAULT CHARSET=latin1 WITH SYSTEM VERSIONING

1 row in set (0.001 sec)

MariaDB [sbtest]> alter table sbtest1 add period for time_period(time_1, time_2);

ERROR 4025 (23000): CONSTRAINT `time_period` failed for `sbtest`.`sbtest1`