ActiveRecord relation with an aliased model doesn't work

aliased_relation_bug.rb

# Activate the gem you are reporting the issue against.
gem 'activerecord', '~> 4.1'
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 do |t|
    t.references :author
  end

  create_table :users do |t|
  end
end

class User < ActiveRecord::Base
  has_many :posts, :inverse_of => :author
end

class Post < ActiveRecord::Base
  Author = User

  belongs_to :author
end

class BugTest < Minitest::Test
  def test_association_stuff
    post = Post.new
    post.build_author
  end
end