`has_many :through` an association that uses `includes` throws an error

has_many_through_includes.rb

# Activate the gem you are reporting the issue against.
gem 'activerecord', '4.1.1' # as well as '4.2.0'
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 :people, force: true do |t|
    t.string :name
  end

  create_table :relationships, force: true do |t|
    t.integer :person_id
    t.integer :other_id
    t.integer :relationship_type_id
  end

  create_table :relationship_types, force: true do |t|
    t.integer :kind
  end
end

class RelationshipType < ActiveRecord::Base
  belongs_to :relationship

  enum kind:[:friend, :family]
end

class Person < ActiveRecord::Base
  has_many :relationships
  has_many :family_relationships, ->{ family }, class_name: "Relationship"
  has_many :types, through: :family_relationships, source: :relationship_type
  has_many :family_members, through: :family_relationships, source: :person
end

class Relationship < ActiveRecord::Base
  belongs_to :relationship_type
  belongs_to :person
  belongs_to :other, class_name: "Person", foreign_key: :other_id

  scope :family, ->{
    includes(:relationship_type).where(relationship_types: { kind: RelationshipType.kinds[:family] })
  }
end

class BugTest < Minitest::Test
  def test_has_many_through_includes
    mike = Person.create! name: "Mike"
    carly = Person.create! name: "Carly"

    # Mike has Carly as a family member
    family_type = RelationshipType.create! kind: RelationshipType.kinds[:family]
    relationship = mike.relationships.create! other: carly, relationship_type: family_type

    # Can find the family relationship
    assert_equal 1, Relationship.family.count
    assert_equal 1, mike.family_relationships.count

    # Should find Carly has a family member but throws an error
    assert_equal carly, mike.family_members.first
  end
end