In PHP 5.3.3 (on Linux 2.6.32-431.23.3.el6.x86_64), there is a related(identical?) bug which causes the last element of an array to be passed/assigned by reference if its parent array is used as a reference. 

For example, foreach ($my_array as &$array_val) {...} will cause the last element of $my_array to be assigned by reference: 

    $my_new_array = $my_array; 
    $my_new_array[4] = null; // if $my_array's last index is 4, this will nullify that value too 

and passed by reference: 

    function dont_touch($param) { // modify $param here } 
    dont_touch($my_array[4]); // $my_array[4] will be modified 

This can be fixed by unsetting the reference to the array value after the foreach loop. 

    unset($array_val); // after the foreach loop

Try running this code and comment/uncomment the line containing "unset". 

<?php 

$thingies = array(array(1,2,3,4),array(1,2,3,4)); 

var_dump($thingies); 

foreach ($thingies as &$things) { 
    foreach ($things as $thing) { 
        $thing += 1; 
    } 
} 

unset($things); 

$copythings = $thingies; 
$copythings[1][0] += 1; 
$copythings[1][1] += 1; 
$copythings[1][2] += 1; 
$copythings[1][3] += 1; 

var_dump($thingies); 

?>

There isn't actually a bug here. This is how references work and there is no change of behaviour from one version to the next. All versions of PHP give the same result here.

Here's the relevant documention showing that this is expected behaviour:
http://php.net/manual/en/language.references.whatdo.php
(search for "Assignment of array variables")