Is getChangedFields() valid?

Suppose I create a table and model like this.

CREATE TABLE tbl
(
    id      INT UNSIGNED      NOT NULL AUTO_INCREMENT,
    type    TINYINT UNSIGNED  NOT NULL DEFAULT 1,
    prefix  TINYINT UNSIGNED  NOT NULL DEFAULT 0,
    PRIMARY KEY (id),
);
INSERT INTO tbl (id, prefix) VALUES(10, 10);

class Tbls extends ModelBase
{
    protected ?int $id     = null;
    protected ?int $type   = 1;
    protected ?int $prefix = 0;
    public function getId() { return $this->id; }
    public function getType() { return $this->type; }
    public function getPrefix() { return $this->prefix; }
}

Then get the row with id = 10.

$mdl = Tbls::findFirst(10);

At this point I haven't changed anything yet, but $mdl->getChangedFields() is ['id', 'type', 'prefix'].

After executing $mdl->assign($ary), I wanted to check if there are any changed items, but this is meaningless. Each value in the snapshot was string, but the $mdl properties are integer.

Normally, all the values obtained by PDO are obtained as character strings regardless of the table settings. So, it makes sense that the snapshot value is a string, but since the property value is an integer when it is acquired by findFirst (), it is said to be "changed". I'm in trouble.