Assignment to element in child array in C++ replaced the whole child array

[hcngac]

in C++,

Php::Array PhpArray;
Php::Array PhpSubArray({"a","b","c","d"});
PhpArray["1111"]["2222"] = PhpSubArray;
Php::call("var_dump", PhpArray);
PhpSubArray[0] = "X";
Php::call("var_dump", PhpArray);
PhpArray["1111"]["2222"][0] = "X";
Php::call("var_dump", PhpArray);

would result in

array(1) {
  [1111]=>
  array(1) {
    [2222]=>
    array(4) {
      [0]=>
      string(1) "a"
      [1]=>
      string(1) "b"
      [2]=>
      string(1) "c"
      [3]=>
      string(1) "d"
    }
  }
}
array(1) {
  [1111]=>
  array(1) {
    [2222]=>
    array(4) {
      [0]=>
      string(1) "a"
      [1]=>
      string(1) "b"
      [2]=>
      string(1) "c"
      [3]=>
      string(1) "d"
    }
  }
}
array(1) {
  [1111]=>
  array(1) {
    [2222]=>
    array(1) {
      [0]=>
      string(1) "X"
    }
  }
}

while in PHP,

$PhpArray = Array();
$PhpSubArray = Array('A','B','C','D');
$PhpArray['1111']['2222'] = $PhpSubArray;
var_dump($PhpArray);
$PhpSubArray[0] = 'X';
var_dump($PhpArray);
$PhpArray['1111']['2222'][0] = 'X';
var_dump($PhpArray);

result in

array(1) {
  [1111]=>
  array(1) {
    [2222]=>
    array(4) {
      [0]=>
      string(1) "A"
      [1]=>
      string(1) "B"
      [2]=>
      string(1) "C"
      [3]=>
      string(1) "D"
    }
  }
}
array(1) {
  [1111]=>
  array(1) {
    [2222]=>
    array(4) {
      [0]=>
      string(1) "A"
      [1]=>
      string(1) "B"
      [2]=>
      string(1) "C"
      [3]=>
      string(1) "D"
    }
  }
}
array(1) {
  [1111]=>
  array(1) {
    [2222]=>
    array(4) {
      [0]=>
      string(1) "X"
      [1]=>
      string(1) "B"
      [2]=>
      string(1) "C"
      [3]=>
      string(1) "D"
    }
  }
}

Is it normal behavior or is it a bug? Thank you!