cannot create an instance of subset type

[Marcel Timmerman]

Hi,

Using the next code I get an error on the instantiation of $d2;

---
use v6;

class ABC {
  method s ( Int $i ) { say $i + 10; }
}

subset DEF of ABC;

my ABC $a .= new;
$a.s(10);   # 20

my DEF $d1 = $a;
$d1.s(11);  # 21

my DEF $d2 .= new;
$d2.s(12);
---

Error is

You cannot create an instance of this type (DEF)
  in block <unit> at xt/subset-test.pl6 line 15

Why is this?

Regards,
Marcel