ruby-on-rails - Rails association touch always edit updated_at although something is not changed

Question

i have serious problem with touch directive in Rails association.

It always edit updated_at timestamp. That is weird because when associated object is not changed, always update timestamp.

Have Place

class Place < ActiveRecord::Base
  has_one     :location,        inverse_of: :place, dependent: :destroy

  attr_accessible :name
  attr_accessible :location_attributes

  accepts_nested_attributes_for :location
end

and Location

class Location < ActiveRecord::Base
  belongs_to :place, inverse_of: :location, touch: true

  attr_accessible :number, :street, :locality, :region, :postal_code, :country, :description, :description_en, :latitude, :longitude
  attr_accessible :place_id

  validates :place,       presence: true
  validates :number,      presence: true
  validates :street,      presence: true
  validates :locality,    presence: true
  validates :postal_code, presence: true, postal_code: { country: :sk }
  validates :latitude,    presence: true, numericality: true, allow_nil: true
  validates :longitude,   presence: true, numericality: true, allow_nil: true
end

When i load and save existed place without changes:

Place.last.save # changed? == false

it automaticaly edit updated_at

SQL (0.4ms)  UPDATE `places` SET `updated_at` = '2012-11-18 20:38:48' WHERE `places`.`id` = 490

Do someone any experience with this how to fix it or something?

Uses Rails 3.2.9 and MySQL (mysql2 adapter)

EDIT:

Location.last.save changed to Place.last.save. It was mistake.