associations do not autosave when a child is modified by creating a "grandchild" thru nested attributes

accepts_nested_attributes_for is fabulous, but we've run into an issue where an object in our hierarchy doesn't save when we think it should.

Here's a test case that fails when added to: autosave_association_test.rb in the rails 2-3-stable branch

Pirate (new object)
  |
  |-> Ship (existing object identified by id)
       |
       |-> ShipPart (new object)

The ShipPart fails to save when saving Pirate. Both Pirate and Ship use accepts_nested_attributes to permit creation of the next lower child via attribute assignments.

Our speculation of the source of this bug is that autosave does not cascade past objects are are not new_record? or whose attributes are not changed?

class TestDeepAutosaveAssociation < ActiveRecord::TestCase
    self.use_transactional_fixtures = false

    def setup
        Ship.accepts_nested_attributes_for :parts

        @ship = Ship.create!(:name => "Bounty")
        assert_not_nil @ship
    end

    def test_that_new_grandchild_will_save_when_child_exists
      assert_difference "Pirate.count", 1 do
        assert_difference "ShipPart.count", 1 do
            assert_no_difference "Ship.count"  do
            @pirate = Pirate.create!(:catchphrase => "Arhh!", 
                            :ship_attributes => { :id => @ship.id,
                                                :parts_attributes => [ {:name => "plank"} ] })
            end
        end
      end

    end


end