undefined method `id_criteria' for Array when submitting Rails 3 form containing more than one instance of a relationally associated mongoid document

mongoid error in rails 3 form

class Person
  include Mongoid::Document
  include Mongoid::Timestamps
  field :name, :type => String
  key :name
  references_many :books, :dependent => :destroy
  accepts_nested_attributes_for :books
end

class Book
  include Mongoid::Document
  include Mongoid::Timestamps
  field :title, :type => String
  referenced_in :person
end

class PeopleController < ApplicationController
  def new
    @person = Person.new
    2.times do
      @person.books << Book.new 
    end
  end
  def create
    @person = Person.new(params[:person])
    respond_to do |format|
      if @person.save
        redirect_to @person, :notice => 'Saved.'
      else
        render :action => "new"
      end
    end
  end
end

= form_for @person  do |f|
  .field
    = f.label :name
    = f.text_field :name
    = f.fields_for :books do |f|
      .field
        = f.text_area :title
  .actions
    = f.submit 'Save'