Unexpected behavior in pluck

pluck_bug.rb

gem 'activerecord', '4.1.0'
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 do |t|
    t.string :name
    t.integer :age
  end

  create_table :pets do |t|
    t.references :person
    t.string :name
    t.string :species
  end
end

class Person < ActiveRecord::Base
  has_many :pets
end

class Pet < ActiveRecord::Base
  belongs_to :person
end

# Setup
peter, sally = Person.create [{ name: "Peter", age: 22 }, { name: "Sally", age: 25 }]

peter.pets.create [{ name: "Pluto", species: "Dog" }, { name: "Garfield", species: "Cat" }]
sally.pets.create [{ name: "Romeo", species: "Cat" }, { name: "Juliet", species: "Cat" }]

EXPECTED = [["Peter", "Garfield"], ["Sally", "Juliet"], ["Sally", "Romeo"]]
# NO_ALIAS = [["Garfield", nil], ["Juliet", nil], ["Romeo", nil]]

class BugTest < Minitest::Test
  def pluck_fails_without_alias
    plucked = Person.joins(:pets)
      .where("pets.species = ?", "Cat")
      .order("people.name ASC, pets.name ASC")
      .pluck("people.name", "pets.name")

    assert_equals plucked, EXPECTED
    # assert_equals plucked, NO_ALIAS
  end

  def pluck_succeeds_with_alias
    plucked = Person.joins(:pets)
      .where("pets.species = ?", "Cat")
      .order("people.name ASC, pets.name ASC")
      .pluck("people.name", "pets.name as pet_name")

    assert_equals plucked, EXPECTED
  end
end