ERROR 1032 (HY000): Can't find record with MyISAM, (too?) large key and DISABLE KEYS

This runs just fine:

CREATE TABLE `test` (

  `id` int unsigned NOT NULL,

  `foo` varchar(255) NOT NULL,

  PRIMARY KEY (`id`),

  UNIQUE KEY `foo_key` (`foo`)

) ENGINE=MyISAM;

INSERT INTO `test` VALUES (1,'dummy');

However, when first disabling keys (commonly seen when using mysqldump) the INSERT query fails with an ERROR 1032 (HY000): Can't find record in 'test':

DROP TABLE IF EXISTS `test`;

CREATE TABLE `test` (

  `id` int unsigned NOT NULL,

  `foo` varchar(255) NOT NULL,

  PRIMARY KEY (`id`),

  UNIQUE KEY `foo_key` (`foo`)

) ENGINE=MyISAM;

ALTER TABLE `test` DISABLE KEYS;

INSERT INTO `test` VALUES (1,'dummy');

Character set being used is utf8mb4

If you use the ARIA storage engine, the CREATE statement will fail with ERROR 1071 (42000): Specified key was too long; max key length is 1000 bytes (varchar(255) in utf8mb4 is 1020 bytes).
If you use the InnoDB storage engine, there is no issue.
If you change the column foo to a varchar(250), it works fine as well.