Perl 6 type check failure for Array of *

A.pm6

use B;

unit class A;

method make_str returns Array of Str {
    Array[Str].new: '' xx 3;
}

B.pm6

unit class B;

has Str @.arr;

script.p6

#!/usr/bin/env perl6

use lib '.';

use A;

say A.new.make_str.perl;