strange_unserialize_behaviour.php

<?php
class A implements Serializable
{
    public function serialize()
    {
        $dt = new \DateTime();
        return serialize([
            $dt,
            serialize([$dt])
        ]);
    }

    public function unserialize($serialized)
    {
        $a = unserialize($serialized);
        unserialize($a[1]);
    }
}

$a = new A();
$s = serialize($a);
$d = unserialize($s);

var_dump($s);