MooseX::ClassAttribute bug/feature?

gistfile1.pl

package My::Base;

use Moose;
use MooseX::ClassAttribute;

class_has 'foo' =>
    ( is      => 'rw',
      isa     => 'Str',
      lazy_build => 1,
    );

sub _build_foo { die "setup in child" };

__PACKAGE__->meta()->make_immutable();

no Moose;
no MooseX::ClassAttribute;

package My::A;
use Moose;
use MooseX::ClassAttribute;
extends 'My::Base';

override '_build_foo' => sub { return 'a' };

package My::B;
use Moose;
use MooseX::ClassAttribute;
extends 'My::Base';

override '_build_foo' => sub { return 'b' };

package main;

my $a = My::A->new();
my $b = My::B->new();

print "A -> " . $a->foo() . "\n";
print "B -> " . $b->foo() . "\n";
--------
>perl test.pl
A -> a
B -> a

Moose version 2.0008
MooseX::ClassAttribute version 0.26