Interesting bug in PHP

Question

Here in the following block of program it prints 2 instead of 1.

<?php
 f(0, $$var);
 $x = 1;
 $y = 2;
 echo $x;
 function f($a, $b) {}
?>

Any suggestions?
UPDATE 1
This information has been get from http://habrahabr.ru/blogs/php/95595
UPDATE 2
By posting this question mainly I just wanted to 1) inform others about this bug, 2) get ideas of different users about the reasons of why this happens.

Answer 1

Prints 2 on Mac. (PHP 5.3.1)