Auto-create: Pre-existing historical data is not partitioned as specified by ALTER

MariaDB [test]> show create table t \G

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

       Table: t

Create Table: CREATE TABLE `t` (

  `pk` int(11) NOT NULL,

  `a` int(11) DEFAULT NULL,

  PRIMARY KEY (`pk`)

) ENGINE=MyISAM DEFAULT CHARSET=latin1 WITH SYSTEM VERSIONING

1 row in set (0.000 sec)

MariaDB [test]> select year(row_end) y, count(*) from t for system_time all group by y;

+------+----------+

| y    | count(*) |

+------+----------+

| 2019 |        8 |

| 2020 |       12 |

| 2021 |        4 |

| 2038 |        2 |

+------+----------+

4 rows in set (0.001 sec)

MariaDB [test]> alter table t partition by system_time interval 1 year auto;

Query OK, 26 rows affected (0.017 sec)             

Records: 26  Duplicates: 0  Warnings: 0

MariaDB [test]> show create table t \G

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

       Table: t

Create Table: CREATE TABLE `t` (

  `pk` int(11) NOT NULL,

  `a` int(11) DEFAULT NULL,

  PRIMARY KEY (`pk`)

) ENGINE=MyISAM DEFAULT CHARSET=latin1 WITH SYSTEM VERSIONING

 PARTITION BY SYSTEM_TIME INTERVAL 1 YEAR STARTS TIMESTAMP'2021-04-26 00:00:00' AUTO

PARTITIONS 2

1 row in set (0.000 sec)

MariaDB [test]> select count(*) from t partition (p0);

+----------+

| count(*) |

+----------+

|       24 |

+----------+

1 row in set (0.000 sec)