[bug?] rails form_for

i think there is a bug in how rails automatically detects if a
form_for should be a post or put when the controller is in a
namespace. can someone confirm this, or am i doing something wrong?

### specs
windows xp
ruby 1.8.6
rails 2.1.1
mysql 5

### in the terminal
rails bug_test
cd bug_test
# edit database.yml
ruby script/generate model User name:string
ruby script/generate controller admin/site_users
rake db:migrate

### config/routes.rb
ActionController::Routing::Routes.draw do |map|
  map.resources :users
  map.namespace :admin do |admin|
    admin.resources :site_users
    admin.resources :roles
  end
end

### controllers/admin/site_users_controller.rb
class Admin::SiteUsersController < ApplicationController
  def index
    @users = User.find(:all)
  end
  def new
    @user = User.new
  end
  def edit
    @user = User.find(params[:id])
  end
  def create
    @user = User.new(params[:user])
    respond_to do |format|
      if @user.save
        flash[:notice] = 'User was successfully created.'
        format.html { redirect_to( admin_site_users_path )}
        format.xml { render :xml => @user, :status
=> :created, :location => @user }
      else
        flash.now[:error] = "We couldn't set up that account."
        format.html { render :action => "new" }
        format.xml { render :xml => @user.errors, :status
=> :unprocessable_entity }
      end
    end
  end
end

### views/admin/site_users/edit.html.erb
<h1> Editing a user erb</h1>
<%= error_messages_for :user %>
<h2>
<% if @user.respond_to?(:new_record?) && @user.new_record? %>
  ERROR => NEW RECORD
<% else %>
  OLD RECORD => form_for method should be put
<% end %>
</h2>
<% form_for(:user, :url => admin_site_user_path ) do |f| %>
  <p><%= label_tag 'name' %> <%= f.text_field :name %></p>
  <p><%= f.submit 'Update' %></p>
<% end %>