Problem with 3-tier delete

When I try to delete a grandfather in a grandfather, father & son
relationship as in the following, the grandfather and all the
associated fathers are deleted, but the sons are left as orphans.
It seems ROR can do a 2-tier cascading delete, but fails on a 3-tier
cascading delete.

create_table “galleries”, :force => true do |t|
t.string “name”
end

create_table “gallery_images”, :force => true do |t|
t.integer “gallery_id”
end

create_table “gallery_image_profiles”, :force => true do |t|
t.integer “gallery_image_id”
t.integer “profile_id”
end

model gallery.rb
class Gallery < ActiveRecord::Base
has_many :gallery_images, :dependent =>:delete_all
end

model gallery_image.rb
class GalleryImage < ActiveRecord::Base
belongs_to :gallery

has_many :gallery_image_profiles, :dependent => :delete_all

end

model gallery_image_profile.rb
class GalleryImageProfile < ActiveRecord::Base
belongs_to :gallery_image
belongs_to :profile
end

controller: galleries_controller.rb
class GalleriesController < ApplicationController
def destroy
@gallery = Gallery.find(params[:id])
@gallery.destroy
redirect_to :action => ‘list’
end
end