Description:
------------
json_encode will parse the PHP array as if it has string keys when a numerical key is unset.
var_dump() shows expected results. So i assume this issue is wit json_encode().

Test script:
---------------
<?
$array = array('a','b','c');

unset($array[0]);

echo json_encode($array);
?>

Expected result:
----------------
["b","c"]

Actual result:
--------------
{"1":"b","2":"c"}