Description:
------------
- The result of clone passed as an argument provokes a recursive reference.
+ The result of clone stored in the variable that is passed as an argument does not cause problems.

Test script:
---------------
function assign(&$r, $c){
  $r = $c; 
}

class A{
  private $c;
  public function run(){
    assign($this->c, clone $this); // this code generates actual result
    
    //$c = clone $this;
    //assign($this->c, $c); this code generates the expected result
  }
}

$o = new A();
$o->run();
var_dump($o);

Expected result:
----------------
object(A)#27 (1) {
  ["c":"A":private]=>
  object(A)#13 (1) {
    ["c":"A":private]=>
    NULL
  }
}

Actual result:
--------------
object(A)#21 (1) {
  ["c":"A":private]=>
  &object(A)#20 (1) {
    ["c":"A":private]=>
    *RECURSION*
  }
}