Description:
------------
Results in PHP 7.1+ and pre-PHP-7.1 are differs. I'm not sure what I have to expect to see but pre-PHP-7.1 result is more intuitive.

Test script:
---------------
$arr = [[1]];

array_walk($arr, function(){});
array_map('array_shift', $arr);
var_dump($arr);


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

Actual result:
--------------
array(1) {
  [0]=>
  array(0) {
  }
}