Rails: has_many :through does not autosave when the parent is new

test_has_many_autosave.rb

gem 'activerecord', '4.2.1'
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:')
ActiveRecord::Base.logger = Logger.new(STDOUT)

ActiveRecord::Schema.define do
  create_table :posts, force: true do |_|
  end

  create_table :catalog_memberships, force: true do |t|
    t.integer :post_id
    t.integer :catalog_id
  end

  create_table :catalogs, force: true do |t|
    t.string :title
  end
end

class Post < ActiveRecord::Base
  has_many :catalog_memberships, inverse_of: :post
  has_many :catalogs, through: :catalog_memberships, inverse_of: :posts, autosave: true
end

class CatalogMembership < ActiveRecord::Base
  belongs_to :post, inverse_of: :catalog_memberships
  belongs_to :catalog, inverse_of: :catalog_memberships
end

class Catalog < ActiveRecord::Base
  has_many :catalog_memberships, inverse_of: :catalog
  has_many :posts, through: :catalog_memberships, inverse_of: :catalogs, autosave: true
end

class BugTest < Minitest::Test
  # This test passes
  def test_autosave_has_many_through_on_existing_parent
    catalog = Catalog.create!(title: 'Original Title')
    catalog.title = 'Amended Title'

    post = Post.create!
    post.catalogs = [catalog]
    post.save!

    assert_equal 1, post.catalogs.count
    assert_equal 'Amended Title', catalog.reload.title
  end

  # This test should also pass, but is instead failing
  def test_autosave_has_many_through_on_new_parent
    catalog = Catalog.create!(title: 'Original Title')
    catalog.title = 'Amended Title'

    post = Post.new
    post.catalogs = [catalog]
    post.save!

    assert_equal 1, post.catalogs.count
    assert_equal 'Amended Title', catalog.reload.title
  end
end