AUTO_INCREMENT breaks after updating a column value to a negative number

MariaDB [test]> select version();

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

| version()           |

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

| 10.2.12-MariaDB-log |

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

1 row in set (0,00 sec)

MariaDB [test]> create table animals (`id` mediumint(9) NOT NULL AUTO_INCREMENT, `name` char(30) NOT NULL, PRIMARY KEY (`id`));

Query OK, 0 rows affected (0,01 sec)

MariaDB [test]> insert into animals (name) values ("dog");

Query OK, 1 row affected (0,00 sec)

MariaDB [test]> select * from animals;

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

| id | name |

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

|  1 | dog  |

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

1 row in set (0,00 sec)

MariaDB [test]> update animals set id=-1 where id=1;

Query OK, 1 row affected (0,00 sec)

Rows matched: 1  Changed: 1  Warnings: 0

MariaDB [test]> select * from animals;

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

| id | name |

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

| -1 | dog  |

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

1 row in set (0,00 sec)

MariaDB [test]> insert into animals (name) values ("cat");

MariaDB [test]> show create table animals;

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

| Table   | Create Table                                                                                                                                                                                    |

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

| animals | CREATE TABLE `animals` (

  `id` mediumint(9) NOT NULL AUTO_INCREMENT,

  `name` char(30) NOT NULL,

  PRIMARY KEY (`id`)

) ENGINE=InnoDB {color:red}AUTO_INCREMENT=18446744073709551615{color} DEFAULT CHARSET=utf8 |

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

1 row in set (0,00 sec)