Description:
------------
After using "array_unshift" (and the first key is numeric) the first (old) key of the array has  changed.

We use PHP 5.2.5 (API 20041225)


Reproduce code:
---------------
$test = array("4711" => "4711", "Hello" => "Hello");
print_r($test);
array_unshift($test, array(null => "New text"));
print_r($test);

Expected result:
----------------
Array ( [4711] => 4711 [Hello] => Hello ) 
Array ( [0] => Array ( [] => New text ) [1] => 4711 [Hello] => Hello ) 

Actual result:
--------------
Array ( [4711] => 4711 [Hello] => Hello ) 
Array ( [0] => Array ( [] => New text ) [4711] => 4711 [Hello] => Hello )