[ Reported in https://rt.cpan.org/Ticket/Display.html?id=58387. ]

If you care to file a bug report or add the missing functionality yourself, here's a test case:

BEGIN {
   package Class;

   use strict;
   use warnings;

   use Moose;

   has val => (
      is       => 'rw',
      isa      => 'Num',
      required => 1,
   );


   use Moose::Util::TypeConstraints;

   coerce __PACKAGE__
      => from 'Num'
         => via { __PACKAGE__->new(val => $_) };
 }


BEGIN {
   package Container;

   use strict;
   use warnings;

   use Moose;

   has always => (
      is      => 'rw',
      isa     => 'Class',
      coerce  => 1,
      default => sub { Class->new(val => 0) },
   );

   has maybe => (
      is      => 'rw',
      isa     => 'Maybe[Class]',
      coerce  => 1,
      default => undef,
   );
}

use strict;
use warnings;

use Test::More tests => 15;


my $always_fail = qr/^Attribute \(always\) does not pass the type cons
+traint/;
my $maybe_fail  = qr/^Attribute \(maybe\) does not pass the type const
+raint/;

my $o = Class->new(val => 123);

eval { Container->new() };                 is($@, '');

eval { Container->new(always => $o) };     is($@, '');
eval { Container->new(always => 123) };    is($@, '');
eval { Container->new(always => "abc") };  like($@, $always_fail);

eval { Container->new(maybe => undef) };   is($@, '');
eval { Container->new(maybe => $o) };      is($@, '');
eval { Container->new(maybe => 123) };     is($@, '');
eval { Container->new(maybe => "abc") };   like($@, $maybe_fail);

my $c = Container->new();

eval { $c->always($o) };     is($@, '');
eval { $c->always(123) };    is($@, '');
eval { $c->always("abc") };  like($@, $always_fail);

eval { $c->maybe(undef) };   is($@, '');
eval { $c->maybe($o) };      is($@, '');
eval { $c->maybe(123) };     is($@, '');
eval { $c->maybe("abc") };   like($@, $maybe_fail);
[download]

Currently failing:

eval { Container->new(maybe => 123) };  is($@, '');
eval { $c->maybe(undef) };              is($@, '');
eval { $c->maybe($o) };                 is($@, '');
eval { $c->maybe(123) };                is($@, '');
eval { $c->maybe("abc") };              like($@, $maybe_fail);
[download]