Celluloid thread issue - threads remain after supervisor is killed

sticky_threads.rb

require 'rubygems'
require 'celluloid'

class DomainWorker
  include Celluloid
  include Celluloid::Logger
  
  def work
    puts "Working..."
  end
end

class DomainSupervisor < Celluloid::SupervisionGroup  
end

class DomainManager
  
  def try_pool
    puts "Starting pool..."
    pool = DomainWorker.pool(size: 5)
    puts "Threads: #{Thread.list.count}"
    
    puts "Terminating pool..."
    pool.terminate
    puts "Threads: #{Thread.list.count}"
  end
  
  def try_pool_and_actor
    puts "Starting pool..."
    pool = DomainWorker.pool
    puts "Threads: #{Thread.list.count}"
    
    puts "Terminating pool..."
    pool.terminate
    
    puts "Creating actor..."
    actor = DomainWorker.new
    puts "Threads: #{Thread.list.count}"
    
    puts "Terminating actor..."
    actor.terminate
    puts "Threads: #{Thread.list.count}"
  end
  
  def run
    puts "Total Actors: #{Celluloid::Actor.all.count}"
    puts "Threads: #{Thread.list.count}"
    
    @supervisor = DomainSupervisor.run!
    @supervisor.pool(DomainWorker, :as => :worker, :size => 10)

    sleep 5
    puts "Threads: #{Thread.list.count}"

    10.times do
      Celluloid::Actor[:worker].async.work
    end

    sleep 5
    puts "Threads: #{Thread.list.count}"

    puts "Finalizing..."
    @supervisor.finalize

    sleep 5
    puts "Threads: #{Thread.list.count}"

    puts "Total Actors: #{Celluloid::Actor.all.count}"
  end
  
end