Rails - Feb 2006 - Confusion with counter and single table inheritance

I''m having trouble getting the magical counter to work in a rails app 
with single table inheritance.

following is the relevant code.

thank you


class declarations

class Job < ActiveRecord::Base
   has_many :vents
end

class Vent < ActiveRecord::Base
   belongs_to :job, :counter_cache => true
   validates_numericality_of :width
end

class Rectangular < Vent
   validates_numericality_of :height
end

table declarations


CREATE TABLE `jobs` (
   `id` int(10) unsigned NOT NULL auto_increment,
   `name` char(40) NOT NULL default '''',
   `user_id` int(11) NOT NULL default ''0'',
   `vents_count` int(11) default ''0'',
   `created_at` timestamp NOT NULL default CURRENT_TIMESTAMP on update 
CURRENT_TIMESTAMP,
   `updated_at` timestamp NOT NULL default ''0000-00-00
00:00:00'',
   `total` decimal(12,2) unsigned default ''0.00'',
   `address_id` int(11) NOT NULL default ''0'',
   PRIMARY KEY  (`id`)
) ENGINE=InnoDB DEFAULT CHARSET=utf8;

CREATE TABLE `vents` (
   `id` int(10) unsigned NOT NULL auto_increment,
   `type` char(20) NOT NULL default '''',
   `width` int(10) unsigned default NULL,
   `height` int(10) unsigned default NULL,
   `rise` int(10) unsigned default NULL,
   `left` tinyint(3) unsigned default NULL,
   `right` tinyint(3) unsigned default NULL,
   `job_id` int(10) unsigned default ''0'',
   `created_at` timestamp NOT NULL default CURRENT_TIMESTAMP on update 
CURRENT_TIMESTAMP,
   `updated_at` timestamp NOT NULL default ''0000-00-00
00:00:00'',
   `price` decimal(10,2) unsigned NOT NULL default ''0.00'',
   `free_area_in` float default NULL,
   `free_area_ft` float default NULL,
   `active` tinyint(3) unsigned default ''1'',
   `flange_id` int(10) unsigned NOT NULL default ''0'',
   `order_id` int(10) unsigned default NULL,
   `quantity` int(10) unsigned NOT NULL default ''1'',
   `square_feet` float default ''0'',
   PRIMARY KEY  (`id`)
) ENGINE=InnoDB DEFAULT CHARSET=utf8;

controller code

def create
       @job = Job.find(session[:job])
       @type = @params[:vent][:type]
       case @type
       when "Rectangular"
	@vent = Rectangular.new(@params[:vent])
  	end
       if @vent.save
         flash[:notice] = ''Vent was successfully created.''
         redirect_to(:controller => ''/store'', :action =>
''show'', :id =>
session[:job])
       else
         render :action => ''new''
       end

       @job.vents << @vent
     end