Problem with STI and scopes

gistfile1.rb

# Let's start off with a company and a buyer model

class Company < ActiveRecord::Base
  has_many :users
end

class Buyer < Company
  # Makes sure that +user+ only gets the buyers she may see.
  # If +user+ is nil we assume anonymous.
  def self.for(user)
    buyers = Buyer.scoped
    if user
      buyers = buyers.where(:id => user.company_id)
    else
      # Some way to make sure nothing is returned
      buyers = buyers.where(:id => 0)
    end
    buyers
  end
end


# Now with standard Rails (no meta_where):
Buyer.for(nil).to_sql
 => "SELECT `companies`.* FROM `companies` WHERE (`companies`.`type` = 'Buyer') AND (companies.id = 0)" 
Buyer.for(nil).where(:id => 2).to_sql
 => "SELECT `companies`.* FROM `companies` WHERE (`companies`.`type` = 'Buyer') AND (companies.id = 0) AND (`companies`.`id` = 2)"

# Now with meta_where included in Gemfile:
Buyer.for(nil).to_sql
 => "SELECT `companies`.* FROM `companies` WHERE (`companies`.`type` = 'Buyer') AND (`companies`.`id` = 0)" 
Buyer.for(nil).where(:id => 2).to_sql
 => "SELECT `companies`.* FROM `companies` WHERE (`companies`.`type` = 'Buyer') AND (`companies`.`id` = 2)" 


# Still testing what exactly causes this issue is caused with STI only...