Possible bug in activerecord has_one

has_one_bug.rb

gem 'activerecord', '4.1.8'
# The behavior is the same with 4.2.0.rc3 as well
# gem 'activerecord', '4.2.0.rc3'
gem 'sqlite3'
require 'active_record'
require 'minitest/autorun'
require 'logger'

# Ensure backward compatibility with Minitest 4
Minitest::Test = MiniTest::Unit::TestCase unless defined?(Minitest::Test)

# This connection will do for database-independent bug reports.
ActiveRecord::Base.establish_connection(adapter: 'sqlite3', database: ':memory:')
# Disable sql logging
# ActiveRecord::Base.logger = Logger.new(STDOUT)

ActiveRecord::Schema.define do
  create_table :posts do |t|
  end

  create_table :comments do |t|
    t.integer :post_id
  end

  create_table :qualities do |t|
    t.integer :post_id
  end
end

class Post < ActiveRecord::Base
  has_many :comments
  has_one :quality
end

class Comment < ActiveRecord::Base
  belongs_to :post
end

class Quality < ActiveRecord::Base
  belongs_to :post
end

class BugTest < Minitest::Test
  def test_new_object_with_has_many
    clear_database
    post = Post.create!
    post.comments << Comment.create!

    new_post = Post.new(id: post.id)
    assert_equal Comment.first, new_post.comments.first
  end

  def test_reloaded_object_with_has_one
    clear_database
    post = Post.create!
    post.quality = Quality.create!

    new_post = Post.new(id: post.id)
    assert_equal Quality.first, new_post.reload.quality
  end

  # This fails
  def test_new_object_with_has_one
    clear_database
    post = Post.create!
    post.quality = Quality.create!

    new_post = Post.new(id: post.id)
    assert_equal Quality.first, new_post.quality
  end

  private

  def clear_database
    Post.destroy_all
    Comment.destroy_all
    Quality.destroy_all
  end
end