Rails - Sep 2009 - Polymorphic form

I have two partials to deal with contact information. The Contact
information uses single-table polymorphism. I want to be able to use
save on Contact and set ''type'' manually, based on the type of
form the
user is filling in. This is saved as the value on a hidden field.

class Contact
  belongs_to :person
  acts_as_list :scope => :person
  validates_presence_of  :type
  validates_inclusion_of :type, :in => TYPES.map {|disp, val| val}
  validates_presence_of  :label
end

class PhoneNumber < Contact
#
# ...
#
  validates_as_phone_number :value
  validates_presence_of :value
  validates_uniqueness_of :value, :scope => [:person_id, :type]
end

class Address < Contact
  validates_presence_of :zip_addon_id
  validates_uniqueness_of :value, :scope => [:person_id, :type]
  belongs_to :zip_addon
end

Here''s one of the partials:
<div class="phone_number">
  <% fields_for "person[contacts][]", phone_number do
|contact_form| -
%>
    <p>
      Phone Number<br/>
      <%= contact_form.hidden_field :type %><br/>
      <%= contact_form.select :label, PhoneNumber::LABELS, :selected
=> PhoneNumber::LABELS.first %>
      Area + Phone <%= contact_form.text_field :value %><br/>
      <%= remove_contact_link :phone_number, ''remove'' %>
    </p>
  <% end -%>
</div>

Everything else gets saved just fine, but it complains on validation
about the lack of a type field:
- Person contacts type can''t be blank

I have it saving like so, in users_controller.rb
  def create
    @user   = User.new(params[:user])
    @person = @user.build_person(params[:user][:person])
    @person.contacts_attributes = params[:person][:contacts]
    if @user.save
      flash[:notice] = ''User was successfully registered.''
      redirect_back_or_default account_url
    else
      render :action => :new
    end
  end

Note also that when I view source on the new user page, the type value
is apparently set appropriately.

Thanks so much.

John