Rails doesn't load fixtures when working with STI

I have these models:

class Company < ActiveRecord::Base
end

class Enterprise < Company
  has_many :establishments
end

class Establishment < Company
  belongs_to :entreprise
end

and these fixtures:

#enterprises.yml
johns_enterprise:
  owner: John
  name: John & co..
  trade: John s Enterprise
  cnpj: 11222333000111

#establishments.yml
josephs_establishment:
  owner: Joseph
  name: Joseph & co..
  trade: Josephsss
  cnpj: 99888777000122

When I run

rake db:fixtures:load

just establishments data are loaded. Anybody knows why?