Multiple (n) identical nested forms generated square-times(n*n) when validation fails - ruby-on-rails-3

Question

User has two addresses shipping(:address_type=0) and billing(:address_type=1)
User form with 2 classic nested forms for each address type are generated square times every submit and failed validation.
Models:
class User < ActiveRecord::Base
has_many :addresses, :dependent => :destroy
accepts_nested_attributes_for :addresses
validates_associated :addresses
end
class Address < ActiveRecord::Base
belongs_to :user
validates :user, :address_type, :first_name, :last_name, :street
end
Controller
class UsersController < ApplicationController
public
def new
#user = User.new
#shipping_address = #user.addresses.build({:address_type => 0})
#billing_address = #user.addresses.build({:address_type => 1})
end
def create
#user = User.new(params[:user])
if #user.save
#fine
else
render => :new
end
end
Uncomplete Form
=form_for #user, :html => { :multipart => true } do |ff|
=ff.fields_for :addresses, #shipping_address do |f|
=f.hidden_field :address_type, :value => 0
=ff.fields_for :addresses, #billing_address do |f|
=f.hidden_field :address_type, :value => 1
=ff.submit

Answer 1

The form should look like this:
=form_for #user, :html => { :multipart => true } do |ff|
=ff.fields_for :addresses do |f|
Nothing else.
Addressess is already a collection, so you should have just one rendering of it.
Also that ":addresses, #shipping_address" makes it to render addresses AND shipping address, even if it's included in #user.addresses.
The addressess built in new action will show there because they are in the addresses collection.
EDIT:
If you need only these two addresses, you can sort it and pass it to fields_for directly:
=form_for #user, :html => { :multipart => true } do |ff|
=ff.fields_for ff.object.addresses.sort{|a,b| a.address_type <=> b.address_type } do |f|
That should do it.

Answer 2

Surprised? I guess not but I was. I found it am I correct? And its stupid and simple.
There is no #shipping_address nor #billing_address when validation fails and rendering the new action (the form) again. But #user has already 2 addresses builded and nested form behave correctly to render each twice for first time failed validation.
def create
#user = User.new(params[:user])
if #user.save
#fine
else
#user.addresses.clear
#user_address = #user.addresses.build({:address_type => 0})
#user_address.attributes = params[:user][:addresses_attributes]["0"]
#billing_address = #user.addresses.build({:address_type => 1})
#billing_address.attributes = params[:user][:addresses_attributes]["1"]
render => :new
end
end