Seralize incorrectly duplicates element in case of circular reference in array

Description

The following code:

<?php

$a = ['id'=>1,'parent'=>null,'child'=>null];
$b = ['id'=>2,'parent'=>null,'child'=>null];
$a['child'] =&$b;
$b['parent'] = &$a;
echo serialize($a);

Resulted in this output:

a:3:{s:2:"id";i:1;s:6:"parent";N;s:5:"child";a:3:{s:2:"id";i:2;s:6:"parent";a:3:{s:2:"id";i:1;s:6:"parent";N;s:5:"child";R:4;}s:5:"child";N;}}

The problem is that in the 'child' array with id 2, 'parent' duplicates the root array with id 1 instead of directly referencing it, something along the lines of :

a:3:{s:2:"id";i:1;s:6:"parent";N;s:5:"child";a:3:{s:2:"id";i:2;s:6:"parent";R:1;s:5:"child";N;}}

In any case, the parent array shouldn't be duplicated, as this can cause traversal issues or modifications that won't properly propagate if code tries to modify the de-serialized array (for instance modifying element 2's parent will not propagate to the root as it should), for instance :

If I modify the original array :

$a['id'] = 3;
echo($a['id'].','.$a['child']['parent']['id']);

echoes (properly) :

3,3

However, if I unserialize the aformentioned string, and apply the same operation, it echoes :

3,1

The reference is lost, as is apparent from the serialized form.

(Of course this is a trivial example but corresponds to something I've encountered working with graph-type arrays)

PHP Version

PHP 8.1.21 (FPM,CLI)

Operating System

Debian 10 x64 (on WSL2 on Windows 10 x64) ; Debian 11 x64 (native)

Commencez par exécuter le reproducteur PHP fourni et comparer la sortie sérialisée avec la forme attendue de référence circulaire. Suivez le comportement de la sérialisation et de la désérialisation des tableaux de PHP pour les références circulaires ; l'issue est terminée lorsque le tableau parent est conservé par référence et que sa modification après la désérialisation se propage à la racine.