Thin Thin → Future

enviromnent
rails (3.2.6)
nginx/1.2.2
thin (1.4.1)

I checked the log file. I found that the 'thin/request' can not be loaded. While i printed the $LOAD_PATH to the log, i found the $LOAD_PATH doesn't contain the thin gem path.
so I add "gem 'thin' " to the Gemfile file of the rails project. then the problem is fixed.

I wonder why i must add "gem 'thin' " to the Gemfile file. Is there a bug?

the log follow:

Writing PID to tmp/pids/thin.0.pid Using rack adapter Thin web server (v1.4.1 codename Chromeo) Maximum connections set to 1024 Listening on /tmp/thin.cellid.0.sock, CTRL+C to stop Exiting! /usr/local/rvm/gems/ruby-1.9.3-p194/gems/thin-1.4.1/lib/thin/connection.rb:31:in post_init': cannot load such file -- thin/request (LoadError) from /usr/local/rvm/gems/ruby-1.9.3-p194/gems/eventmachine-0.12.10/lib/em/connection.rb:45:inblock in new' from /usr/local/rvm/gems/ruby-1.9.3-p194/gems/eventmachine-0.12.10/lib/em/connection.rb:36:in instance_eval' from /usr/local/rvm/gems/ruby-1.9.3-p194/gems/eventmachine-0.12.10/lib/em/connection.rb:36:innew' from /usr/local/rvm/gems/ruby-1.9.3-p194/gems/eventmachine-0.12.10/lib/eventmachine.rb:1430:in event_callback' from /usr/local/rvm/gems/ruby-1.9.3-p194/gems/eventmachine-0.12.10/lib/eventmachine.rb:256:inrun_machine' from /usr/local/rvm/gems/ruby-1.9.3-p194/gems/eventmachine-0.12.10/lib/eventmachine.rb:256:in run' from /usr/local/rvm/gems/ruby-1.9.3-p194/gems/thin-1.4.1/lib/thin/backends/base.rb:63:instart' from /usr/local/rvm/gems/ruby-1.9.3-p194/gems/thin-1.4.1/lib/thin/server.rb:159:in start' from /usr/local/rvm/gems/ruby-1.9.3-p194/gems/thin-1.4.1/lib/thin/controllers/controller.rb:86:instart' from /usr/local/rvm/gems/ruby-1.9.3-p194/gems/thin-1.4.1/lib/thin/runner.rb:185:in run_command' from /usr/local/rvm/gems/ruby-1.9.3-p194/gems/thin-1.4.1/lib/thin/runner.rb:151:inrun!' from /usr/local/rvm/gems/ruby-1.9.3-p194/gems/thin-1.4.1/bin/thin:6:in <top (required)>' from /usr/local/rvm/gems/ruby-1.9.3-p194/bin/thin:20:inload' from /usr/local/rvm/gems/ruby-1.9.3-p194/bin/thin:20:in <main>' from /usr/local/rvm/gems/ruby-1.9.3-p194/bin/ruby_noexec_wrapper:14:ineval' from /usr/local/rvm/gems/ruby-1.9.3-p194/bin/ruby_noexec_wrapper:14:in `'