config.active_record.observers breaks rake tasks

app-models-user.rb

class User < ActiveRecord::Base
end

app-models-user_observer.rb

class UserObserver < ActiveRecord::Observer
end

config-application.rb

module Tmp
  class Application < Rails::Application
    #...
    config.active_record.observers = :user_observer
    #...
  end
end

error log

$ rake user:count
rake aborted!
Expected app/models/user.rb to define User

Gemfile.lock

GIT
  remote: git://github.com/rails/rails.git
  revision: 45e85c358d07b90fc52136c51a4511158e51849e
  specs:
    actionmailer (3.2.0.rc1)
      actionpack (= 3.2.0.rc1)
      mail (~> 2.3.0)
    actionpack (3.2.0.rc1)
      activemodel (= 3.2.0.rc1)
      activesupport (= 3.2.0.rc1)
      builder (~> 3.0.0)
      erubis (~> 2.7.0)
      journey (~> 1.0.0.rc1)
      rack (~> 1.3.5)
      rack-cache (~> 1.1)
      rack-test (~> 0.6.1)
      sprockets (~> 2.1.2)
    activemodel (3.2.0.rc1)
      activesupport (= 3.2.0.rc1)
      builder (~> 3.0.0)
    activerecord (3.2.0.rc1)
      activemodel (= 3.2.0.rc1)
      activesupport (= 3.2.0.rc1)
      arel (~> 3.0.0.rc1)
      tzinfo (~> 0.3.29)
    activeresource (3.2.0.rc1)
      activemodel (= 3.2.0.rc1)
      activesupport (= 3.2.0.rc1)
    activesupport (3.2.0.rc1)
      i18n (~> 0.6)
      multi_json (~> 1.0)
    rails (3.2.0.rc1)
      actionmailer (= 3.2.0.rc1)
      actionpack (= 3.2.0.rc1)
      activerecord (= 3.2.0.rc1)
      activeresource (= 3.2.0.rc1)
      activesupport (= 3.2.0.rc1)
      bundler (~> 1.0)
      railties (= 3.2.0.rc1)
    railties (3.2.0.rc1)
      actionpack (= 3.2.0.rc1)
      activesupport (= 3.2.0.rc1)
      rack-ssl (~> 1.3.2)
      rake (>= 0.8.7)
      rdoc (~> 3.4)
      thor (~> 0.14.6)

GEM
  remote: http://rubygems.org/
  specs:
    ansi (1.4.1)
    arel (3.0.0.rc1)
    builder (3.0.0)
    coffee-rails (3.2.0)
      coffee-script (>= 2.2.0)
      railties (~> 3.2.0.beta)
    coffee-script (2.2.0)
      coffee-script-source
      execjs
    coffee-script-source (1.2.0)
    erubis (2.7.0)
    execjs (1.2.13)
      multi_json (~> 1.0)
    hike (1.2.1)
    i18n (0.6.0)
    journey (1.0.0.rc1)
    jquery-rails (1.0.19)
      railties (~> 3.0)
      thor (~> 0.14)
    json (1.6.3)
    mail (2.3.0)
      i18n (>= 0.4.0)
      mime-types (~> 1.16)
      treetop (~> 1.4.8)
    mime-types (1.17.2)
    multi_json (1.0.4)
    polyglot (0.3.3)
    rack (1.3.5)
    rack-cache (1.1)
      rack (>= 0.4)
    rack-ssl (1.3.2)
      rack
    rack-test (0.6.1)
      rack (>= 1.0)
    rake (0.9.2.2)
    rdoc (3.12)
      json (~> 1.4)
    sass (3.1.12)
    sass-rails (3.2.1)
      railties (~> 3.2.0.beta)
      sass (>= 3.1.10)
      tilt (~> 1.3)
    sprockets (2.1.2)
      hike (~> 1.2)
      rack (~> 1.0)
      tilt (~> 1.1, != 1.3.0)
    sqlite3 (1.3.5)
    thor (0.14.6)
    tilt (1.3.3)
    treetop (1.4.10)
      polyglot
      polyglot (>= 0.3.1)
    turn (0.8.3)
      ansi
    tzinfo (0.3.31)
    uglifier (1.2.0)
      execjs (>= 0.3.0)
      multi_json (>= 1.0.2)

PLATFORMS
  ruby

DEPENDENCIES
  coffee-rails
  jquery-rails
  rails!
  sass-rails
  sqlite3
  turn
  uglifier

lib-tasks-count_user.rake

namespace :user do
  desc "count user"
  task :count => :environment do
    p User.count
  end
end