ActiveRecord::Base#cloneは本当はcloneではなかったらしい

freezeはコピーされない

Object#clone

>> class A
>> end
=> nil
>> a = A.new
=> #<A:0x2480948>
>> a.taint
=> #<A:0x2480948>
>> a.freeze
=> #<A:0x2480948>
>> a.tainted?
=> true
>> a.frozen?
=> true
>> b = a.clone
=> #<A:0x244d55c>
>> b.tainted?
=> true
>> b.frozen?
=> true

ActiveRecord::Base#clone

?> obj1 = Article.new
=> #<Article id: nil, title: nil, body: nil, created_at: nil, updated_at: nil>
>> obj1.taint
=> #<Article id: nil, title: nil, body: nil, created_at: nil, updated_at: nil>
>> obj1.freeze
=> #<Article id: nil, title: nil, body: nil, created_at: nil, updated_at: nil>
>> obj1.tainted?
=> true
>> obj1.frozen?
=> true
>> obj2 = obj1.clone
=> #<Article id: nil, title: nil, body: nil, created_at: nil, updated_at: nil>
>> obj2.tainted?
=> false
>> obj2.frozen?
=> false

特異メソッドもコピーされない

Object#clone

>> a = A.new
=> #<A:0x2480948>
>> class << a
>>   def hello
>>     "hello"
>>   end
>> end
=> nil
>> b = a.clone
=> #<A:0x247b81c>
>> a.hello
=> "hello"
>> b.hello
=> "hello"

ActiveRecord::Base#clone

?> obj1 = Article.new
=> #<Article id: nil, title: nil, body: nil, created_at: nil, updated_at: nil>
>> class << obj1
>>   def hello
>>    "hello"
>>   end
>> end
=> nil
>> obj2 = obj1.clone
=> #<Article id: nil, title: nil, body: nil, created_at: nil, updated_at: nil>
>> obj1.hello
=> "hello"
>> obj2.hello
NoMethodError: undefined method `hello' for #<Article:0x23c4ef0>
        from /Users/sogo/code/rails/edge_rails/vendor/rails/activerecord/lib/../../activemodel/lib/active_model/attribute_methods.rb:240:in `method_missing'
        from /Users/sogo/code/rails/edge_rails/vendor/rails/activerecord/lib/active_record/attribute_methods.rb:38:in `method_missing'
        from (irb):26

インスタンス変数をコピーしているだけですね
activerecord/lib/active_record/base.rb

      # Returns a clone of the record that hasn't been assigned an id yet and
      # is treated as a new record.  Note that this is a "shallow" clone:
      # it copies the object's attributes only, not its associations.
      # The extent of a "deep" clone is application-specific and is therefore
      # left to the application to implement according to its need.
      def clone
        attrs = clone_attributes(:read_attribute_before_type_cast)
        attrs.delete(self.class.primary_key)
        record = self.class.new
        record.send :instance_variable_set, '@attributes', attrs
        record
      end