If a cyclic model is namespaced, root and parent relationships are lost

namespaced.rb

require 'mongoid'
require 'minitest/autorun'

Mongoid.configure do |config|
  config.master = Mongo::Connection.new.db('nodes_test')
end

module Tree
  class Node
    include Mongoid::Document

    recursively_embeds_many

    field :name

    def is_root?
      parent_node.nil?
    end

  end
end

class NodeTest < MiniTest::Unit::TestCase

  include Tree

  def setup
    @root = Node.new(name: 'root')
    @first_child = @root.child_nodes.build(name: 'first_child')
    @second_child = @root.child_nodes.build(name: 'second_child')
    @root.save!
  end

  def test_a_node_knows_if_it_is_a_root
    assert @root.is_root?
  end

  def test_a_node_knows_if_it_not_a_root
    refute @root.child_nodes.first.is_root?
  end

  def test_a_node_knows_its_parent
    assert_equal @root, @root.child_nodes.first.parent_node
  end

end

not-namespaced.rb

require 'mongoid'
require 'minitest/autorun'

Mongoid.configure do |config|
  config.master = Mongo::Connection.new.db('nodes_test')
end

class Node
  include Mongoid::Document

  recursively_embeds_many

  field :name

  def is_root?
    parent_node.nil?
  end

end

class NodeTest < MiniTest::Unit::TestCase

  def setup
    @root = Node.new(name: 'root')
    @first_child = @root.child_nodes.build(name: 'first_child')
    @second_child = @root.child_nodes.build(name: 'second_child')
    @root.save!
  end

  def test_a_node_knows_if_it_is_a_root
    assert @root.is_root?
  end

  def test_a_node_knows_if_it_not_a_root
    refute @root.child_nodes.first.is_root?
  end

  def test_a_node_knows_its_parent
    assert_equal @root, @root.child_nodes.first.parent_node
  end

end