PHP refcount bug

gistfile1.php

<?php
class B {
	static public $instances = [];

	public function __destruct()
	{
		echo "Object B destructed!";
	}
}

$b = new B; // Here positive testing
B::$instances[spl_object_hash($b)] = &$b;
xdebug_debug_zval('b');
echo "Expecting object destruction ... ";
$b = false; // Object destructed here as expected;
echo " Expectation finished\n";

class A {

	static public $instances = [];

	public function __construct()
	{
		self::$instances[spl_object_hash($this)] = &$this;
	}

	public function __destruct()
	{
		echo "Object A destructed!";
	}
}

$a = new A; // Here negative testing
xdebug_debug_zval('a');
echo " Expecting object destruction ... ";
gc_collect_cycles();
$a = false; // Object is not destructed here.
echo " Expectation finished\n";

echo "End of script\n";