.last sort conundrum

script.rb

# Activate the gem you are reporting the issue against.
# gem install activerecord -v '3.2.19'
gem 'activerecord', '3.2.19'
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 |t|
    t.string :name
  end
end

class Post < ActiveRecord::Base
  has_many :comments
end

class BugTest < Minitest::Test
  def test_last_stuff
    10.times { Post.create!(name: rand(9999).to_s) }
    records = Post.find(10, 5, 7, 9, 3)

    assert_equal records.last, records[4]
  end

  def test_default_scope
    10.times { Post.create!(name: rand(9999).to_s) }
    records = Post.order(:name).where(id: [10, 5, 7, 9, 3])

    assert_equal records.last, records[4]
  end
end