Description:
------------
If an array is unserialized where a numerical key is represented as a string (s:3:"123"), the key and its value become inaccessible via direct access ($array[123]) as well as via isset, is_*, array_key_exists, var_dump, etc. The key and value are accessible via var_dump of the whole array, or via foreach.

Reproduce code:
---------------
<?php
$bob = unserialize('a:1:{s:5:"words";a:1:{s:3:"123";s:3:"foo";}}');
echo var_dump($bob);
echo var_dump($bob['words']['123']);
$id1 = '123';
echo var_dump($bob['words'][$id1]);
$id2 = 123;
echo var_dump($bob['words'][$id2]);
echo 0+isset($bob['words']['123']),0+isset($bob['words'][$id1]),0+isset($bob['words'][$id2]);
echo 0+array_key_exists('123',$bob['words']),0+array_key_exists($id1,$bob['words']),0+array_key_exists($id2,$bob['words']);
?>

Expected result:
----------------
array(1) {
  ["words"]=>
  array(1) {
    [123]=>
    string(3) "foo"
  }
}
string(3) "foo"
string(3) "foo"
string(3) "foo"
111111

- OR -

array(1) {
  ["words"]=>
  array(1) {
    ["123"]=>
    string(3) "foo"
  }
}
string(3) "foo"
string(3) "foo"
string(3) "foo"
111111

Actual result:
--------------
array(1) {
  ["words"]=>
  array(1) {
    ["123"]=>
    string(3) "foo"
  }
}
NULL
NULL
NULL
000000