Description:
------------
hundreds of thousands of "$a[]= ..." and "array_pop()" calls triggers memory overwrite.

Reproduce code:
---------------
<?php

$a = array(0,1,2,3,4,5,6,7,8,9,10);

$paths = array();

$stack = array();
for($i=0; $i<100000; $i++) {
    $steps = mt_rand(2,6);
    // move forward
    for($j=0; $j<$steps; $j++) { $stack[] = array('x'=>$a[$j]); }
    $paths[] = $stack;
    // move backward
    for($j=0; $j<$steps; $j++) { array_pop($stack); }
}

print_r($a);

?>

Expected result:
----------------
array $a is never modified in the code, but when you print it at the end of the script it spills out a whole lot of unexpected reccursions or just dies with no output.