counter_cache not updating on update_attributes

When trying to use a simple case of cache_counter:

  class Registration < ActiveRecord::Base
    belongs_to :section, :counter_cache => :registrations_count
  end

  class Section < ActiveRecord::Base
    has_many :registrations
  end

and i wanted to test the scenario where i change the section id on a registration record, if the old one's counter cache will -1 and the new one will +1.

here's the test:

  def test_registration_update_changes_section_counts_when_update_attributes
    sec1 = Section.create! :name => "foo"
    sec2 = Section.create! :name => "bar"
    
    r = Registration.create! :name => "foo", :section => sec1
    sec1.reload
    puts "Section 1 registrations: " + sec1.registrations_count.to_s
  
    assert_equal 1, sec1.registrations_count
    
    r.update_attributes(:section_id => sec2) 
    sec1.reload
    puts "Section 1 after reduce: " + sec1.reload.registrations_count.to_s
    assert_equal 0, sec1.registrations_count
    sec2.reload
    assert_equal 1, sec2.registrations_count
  end

which fails.

The patch applies on 2-3-stable (pulled today) but i am uncertain it's the right way to solve it. i'll wait for the discussion here and create a master patch based on comments.