Reaper pattern in Akka sends its Terminated message to dead letter box - scala

Question

I've been trying the reaper pattern suggested by the Akka team. It does sound good in theory, but the provided unit test does not pass in either sbt or Eclipse's JUnit runner.
import scala.concurrent.duration._
import akka.util.Timeout
import akka.actor._
import akka.testkit.{TestKit, ImplicitSender, TestProbe}
import org.scalatest.{WordSpec, BeforeAndAfterAll}
import org.scalatest.matchers.MustMatchers
import org.scalatest.junit.JUnitRunner
import org.junit.runner.RunWith
#RunWith(classOf[JUnitRunner])
class ReaperSpec extends TestKit(ActorSystem("ReaperSpec"))
with ImplicitSender with WordSpec with BeforeAndAfterAll with MustMatchers
{
import Reaper._
override def afterAll() {
system.shutdown()
}
// Our test reaper. Sends the snooper a message when all the souls have been reaped
private class TestReaper(snooper: ActorRef) extends Reaper {
def allSoulsReaped(): Unit = snooper ! "Dead"
}
"Reaper" should {
"work" in {
// Set up some dummy Actors
val a = TestProbe()
val b = TestProbe()
val c = TestProbe()
val d = TestProbe()
// Build our reaper
val reaper = system.actorOf(Props(new TestReaper(testActor)))
// Watch a couple
reaper ! WatchMe(a.ref)
reaper ! WatchMe(d.ref)
// Stop them
system.stop(a.ref)
system.stop(d.ref)
// Make sure we've been called
within (1 seconds, 5 seconds) {
expectMsg("Dead")
}
}
}
}
After adding logging to the actors, I noticed that the Terminated message ended up in the dead letter box. So the reaper actor never got the Terminated message.
[ERROR] [08/05/2014 11:10:27.244] [ReaperSpec-akka.actor.default-dispatcher-4]
[akka://ReaperSpec/user/$a] Monitored actor [Actor[akka://ReaperSpec/system/testActor2#-1060476766]] terminated (akka.actor.DeathPactException)
[INFO] [08/05/2014 11:10:27.248] [ReaperSpec-akka.actor.default-dispatcher-2]
[akka://ReaperSpec/user/$a] Message [akka.actor.Terminated] from Actor[akka://ReaperSpec/system/testActor5#2029818496] to Actor[akka://ReaperSpec/user/$a#1787786349] was not delivered.
[1] dead letters encountered, no more dead letters will be logged. This logging can be turned off or adjusted with configuration settings 'akka.log-dead-letters' and 'akka.log-dead-letters-during-shutdown'.
I thought that system.stop(watchedActorRef) would guarantee delivery of a Terminated message to all the actors that are watching the watchedActorRef. What am I missing?