Problem with touch and autosave options

Hello,

I face a problem using the new Rails 2.3.3 :touch option along with
the :autosave option.

My app have three models: User, Group and Membership

class User < ActiveRecord::Base
  # attribute: name

  has_many :memberships, :dependent => :destroy
  accepts_nested_attributes_for :memberships, :allow_destroy =>
true, :reject_if => proc { |attributes| attributes
['group_id'].blank? }
  # Having "accepts_nested_attributes_for :memberships"
makes :autosave option true for the "has_many :memberships"
association.
  has_many :groups, :through => :memberships
end

class Membership < ActiveRecord::Base
  # attributes: user_id, group_id, content
  belongs_to :user, :touch => true
  belongs_to :group, :touch => true
end

class Group < ActiveRecord::Base
  # attribute: name
  has_many :memberships, :dependent => :destroy
  has_many :users, :through => :memberships
end

You can see my problem in this console script:

user = User.find 1

  User Load (1.6ms) SELECT * FROM "users" WHERE ("users"."id" = 1)