Description:
------------
When the initial one element array, starting with -1 index, is poped, and afterwards two values are pushed into the obtained empty array, the second value index is becoming 2147483647, which is obviously an error.


All other starting indexes (-2, 0, 1, 2,...) do not affect array in this way. 

Also, when starting index is > 0, the index of the first element, pushed into the empty array is kept from the previous key-value pair. Such behaviour may be also considered erroneous.

Test script:
---------------
<?php
$b=array(-1=>0);
$c=array_pop($b); assert($c == 0);

assert(array_push($b, 0), 1);
assert(array_push($b, 0), 2);
var_dump($b);
assert(array_push($b, 0), 3);
?>

Expected result:
----------------
array(2) {
  [0]=>
  int(0)
  [1]=>
  int(0)
}

Actual result:
--------------
array(2) {
  [-1]=>
  int(0)
  [2147483647]=>
  int(0)
}
PHP Warning:  array_push(): Cannot add element to the array as the next element is already occupied in /home/dmitri/workspace/cell/temp/array_push_pop_bug.php on line 8