PHP Trap in Functions with static variables

static-trap.php

<?php

class A
{
    function __construct()
    {
        echo get_class($this->getInstance()), PHP_EOL,
		get_class(static::getInstance()), PHP_EOL,
		get_class(self::getInstance()), PHP_EOL;
    }

    public static function getInstance()
    {
        static $getInstance;

        if (null == $getInstance) $getInstance = static::makeInstance();

        return $getInstance;
    }

    public static function makeInstance()
    {
        return new stdClass();
    }
}

$a = new A();

class B extends A
{
    function __construct()
    {
        echo get_class($this->getInstance()), PHP_EOL,
		get_class(static::getInstance()), PHP_EOL,
		get_class(self::getInstance()), PHP_EOL;
    }

    public static function makeInstance()
    {
        return new ArrayObject();
    }

    public function __destruct()
    {
        die();
    }
}

$a = new B();