Php Serializable bug

0-test.php

<?php
// The root container object
class Root implements Serializable {
	private $nodes;
	private $mainNode;

	public function __construct() {
		$this->nodes = new IdentifierMap();
	}
	// Adds child object
	public function addNode(Identifier $id, $value) {
		$newNode = new Node($value);

		$this->nodes[$id] = $newNode;

		return $newNode;
	}
	// sets some property
	public function setMainNode(Identifier $id) {
		$this->mainNode = $id;
	}
	public function serialize() {
		return serialize([
			$this->nodes,  
			$this->mainNode,     
		]);
	}
	public function unserialize($data) {
		list(
			$this->nodes,   
			$this->mainNode,
		) = unserialize($data);
	}
}
// Some child object of the root
// stores some value
class Node implements Serializable {
	private $value;
	private $props;
	private $mainProp = NULL;

	public function __construct($value) {
		$this->props = new IdentifierMap();
		$this->value = $value;
	}

	public function serialize() {
		return serialize([
			$this->props,
			$this->value,
			$this->mainProp,
		]);
	}

	public function unserialize($data) {
		list(
			$this->props,
			$this->value,
			$this->mainProp,
		) = unserialize($data);
	}

	public function defineProp(Identifier $id, $val) {
		$this->props[$id] = $val; 
	}

	public function setMainProp(Identifier $id) {
		$this->mainProp = $id;
	}
}
final class IdentifierMap extends SplObjectStorage implements Serializable {
	public function getHash($o) {
		return $o->hash();
	}

	public function serialize() {
		return serialize([
			'parent' => parent::serialize()
		]);
	}

	public function unserialize($data) {
		parent::unserialize(unserialize($data)['parent']);
	}
}

final class Identifier implements Serializable {
	private $name;
	public function __construct($name) {
		if(!is_string($name)) {
			throw new \Exception(sprintf("Identifier must be a string %s given", gettype($name)));
		}
		$this->name = $name;
	}
	public function __toString() {
		return $this->name;
	}
	public function hash() {
		return $this->name;
	}
	public function serialize() {
		return serialize($this->name);
	}
	public function unserialize($data) {
		$this->name = unserialize($data);
	}
}
echo "<pre>";
$root = new Root();
foreach (['fooNode','mainNode'] as $name) {
	$reusedNodeId = new Identifier($name);
	$node = $root->addNode($reusedNodeId, 'some value');
	if($name == 'mainNode') {
		$root->setMainNode($reusedNodeId);
		// if in the call above ^ $reusedNodeId is cloned it works fine
	}

	foreach(['fooProp','mainProp'] AS $prop) {
		$reusedPropId = new Identifier($prop);
		$node->defineProp($reusedPropId, 'propValue');
		if($prop === 'mainProp') {
			$node->setMainProp($reusedPropId);
			// if in the call above ^ $reusedPropId is cloned it works fine
		}
	}
}


$unserializedRoot = unserialize(serialize($root));
echo "Expected:\n";
var_dump($root);
echo "Actual:\n";
var_dump($unserializedRoot);

1-expected.txt

Expected:
object(Root)#1 (2) {
  ["nodes":"Root":private]=>
  object(IdentifierMap)#2 (1) {
    ["storage":"SplObjectStorage":private]=>
    array(2) {
      ["000000003acf8fd20000000051ee4838"]=>
      array(2) {
        ["obj"]=>
        object(Identifier)#3 (1) {
          ["name":"Identifier":private]=>
          string(7) "fooNode"
        }
        ["inf"]=>
        object(Node)#4 (3) {
          ["value":"Node":private]=>
          string(10) "some value"
          ["props":"Node":private]=>
          object(IdentifierMap)#5 (1) {
            ["storage":"SplObjectStorage":private]=>
            array(2) {
              ["000000003acf8fd70000000051ee4838"]=>
              array(2) {
                ["obj"]=>
                object(Identifier)#6 (1) {
                  ["name":"Identifier":private]=>
                  string(7) "fooProp"
                }
                ["inf"]=>
                string(9) "propValue"
              }
              ["000000003acf8fd60000000051ee4838"]=>
              array(2) {
                ["obj"]=>
                object(Identifier)#7 (1) {
                  ["name":"Identifier":private]=>
                  string(8) "mainProp"
                }
                ["inf"]=>
                string(9) "propValue"
              }
            }
          }
          ["mainProp":"Node":private]=>
          object(Identifier)#7 (1) {
            ["name":"Identifier":private]=>
            string(8) "mainProp"
          }
        }
      }
      ["000000003acf8fd90000000051ee4838"]=>
      array(2) {
        ["obj"]=>
        object(Identifier)#8 (1) {
          ["name":"Identifier":private]=>
          string(8) "mainNode"
        }
        ["inf"]=>
        object(Node)#9 (3) {
          ["value":"Node":private]=>
          string(10) "some value"
          ["props":"Node":private]=>
          object(IdentifierMap)#10 (1) {
            ["storage":"SplObjectStorage":private]=>
            array(2) {
              ["000000003acf8fda0000000051ee4838"]=>
              array(2) {
                ["obj"]=>
                object(Identifier)#11 (1) {
                  ["name":"Identifier":private]=>
                  string(7) "fooProp"
                }
                ["inf"]=>
                string(9) "propValue"
              }
              ["000000003acf8fdd0000000051ee4838"]=>
              array(2) {
                ["obj"]=>
                object(Identifier)#12 (1) {
                  ["name":"Identifier":private]=>
                  string(8) "mainProp"
                }
                ["inf"]=>
                string(9) "propValue"
              }
            }
          }
          ["mainProp":"Node":private]=>
          object(Identifier)#12 (1) {
            ["name":"Identifier":private]=>
            string(8) "mainProp"
          }
        }
      }
    }
  }
  ["mainNode":"Root":private]=>
  object(Identifier)#8 (1) {
    ["name":"Identifier":private]=>
    string(8) "mainNode"
  }
}

2-actual.txt

Actual:
object(Root)#13 (2) {
  ["nodes":"Root":private]=>
  object(IdentifierMap)#14 (1) {
    ["storage":"SplObjectStorage":private]=>
    array(2) {
      ["000000003acf8fde0000000051ee4838"]=>
      array(2) {
        ["obj"]=>
        object(Identifier)#15 (1) {
          ["name":"Identifier":private]=>
          string(7) "fooNode"
        }
        ["inf"]=>
        object(Node)#16 (3) {
          ["value":"Node":private]=>
          string(10) "some value"
          ["props":"Node":private]=>
          object(IdentifierMap)#17 (1) {
            ["storage":"SplObjectStorage":private]=>
            array(2) {
              ["000000003acf8fc30000000051ee4838"]=>
              array(2) {
                ["obj"]=>
                object(Identifier)#18 (1) {
                  ["name":"Identifier":private]=>
                  string(7) "fooProp"
                }
                ["inf"]=>
                string(9) "propValue"
              }
              ["000000003acf8fc20000000051ee4838"]=>
              array(2) {
                ["obj"]=>
                object(Identifier)#19 (1) {
                  ["name":"Identifier":private]=>
                  string(8) "mainProp"
                }
                ["inf"]=>
                string(9) "propValue"
              }
            }
          }
          ["mainProp":"Node":private]=>
          int(2)             <<<<<<<<<<<<<<<<< note that mainProp is an integer and not an Identifier value
        }
      }
      ["000000003acf8fc50000000051ee4838"]=>
      array(2) {
        ["obj"]=>
        object(Identifier)#20 (1) {
          ["name":"Identifier":private]=>
          string(8) "mainNode"             
        }
        ["inf"]=>
        object(Node)#21 (3) {
          ["value":"Node":private]=>
          string(10) "some value"
          ["props":"Node":private]=>
          object(IdentifierMap)#22 (1) {
            ["storage":"SplObjectStorage":private]=>
            array(2) {
              ["000000003acf8fc60000000051ee4838"]=>
              array(2) {
                ["obj"]=>
                object(Identifier)#23 (1) {
                  ["name":"Identifier":private]=>
                  string(7) "fooProp"
                }
                ["inf"]=>
                string(9) "propValue"
              }
              ["000000003acf8fc90000000051ee4838"]=>
              array(2) {
                ["obj"]=>
                object(Identifier)#24 (1) {
                  ["name":"Identifier":private]=>
                  string(8) "mainProp"
                }
                ["inf"]=>
                string(9) "propValue"
              }
            }
          }
          ["mainProp":"Node":private]=>
          int(2)                <<<<<<<<<<<<<<<<< note that mainProp is an integer and not an Identifier value
        }
      }
    }
  }
  ["mainNode":"Root":private]=>
  string(10) "some value"            <<<<<<<<<<<<<<<<< note that mainNode is a string and not an IdentifierObject
}