named_scope and habtm chaining problem

Can anyone help me with this?

I have a habtm relationship. I defined a named_scope on one side of it. It works fine except when I chain it. For example:

[code] class Category < ActiveRecord::Base   has_and_belongs_to_many :items end

class Item < ActiveRecord::Base   has_and_belongs_to_many :categories

  named_scope :cat, lambda {|cat| {:include => :categories, :conditions => ["categories.id = ?", cat]}} end [/code]

Simple. Easy. Normal, right?

But, let's see I have the following in my join table "categories_items": category_id | item_id