Description:
------------
Bug converting json_decoded-d object to array. First seen in PHP 5.4. Confirmed in PHP 5.6.15.

See the test script. 

We have a simple array $a. Next we convert it to JSON and back. But after transcoding we can not access the array's values and get NULL or "Notice: Undefined offset: 1".

If replace the line "$a = (array)json_decode(json_encode($a));" with "$a = (array)((object)$a);" everything is OK, converted array's values are accessible.

The test script output is:

array(2) {
  [1] =>
  string(7) "value 1"
  [2] =>
  string(7) "value 2"
}
string(7) "value 1"
string(7) "value 1"

array(2) {
  '1' =>
  string(7) "value 1"
  '2' =>
  string(7) "value 2"
}
NULL
NULL

Test script:
---------------
<?

error_reporting(0);

$a = ['1' => 'value 1', '2' => 'value 2'];
var_dump($a);
var_dump($a[1]);
var_dump($a['1']);

$a = (array)json_decode(json_encode($a));

var_dump($a);
var_dump($a[1]);
var_dump($a['1']);
?>

Expected result:
----------------
The values of the converted array must be accessible

Actual result:
--------------
NULL or Notice: Undefined offset: 1