Class attributes bug?

test.rb

require 'active_support/all'
require 'minitest/autorun'

class A 
  class_attribute :x, default: {}
end 

class B < A 

end 

class C < A

end

C.x[:y] = 1

class ClassAttributesBugTest < Minitest::Test
  def test_subclasses_get_own_hash
    refute_equal(B.x.object_id, C.x.object_id)
  end 

  def test_modifying_classes
    refute_equal(B.x[:y], 1)
  end 

  def test_modifying_classes_effects_parent
    refute_equal(A.x[:y], 1)
  end 
end

All three tests are failing.