Akka drops error logs on ActorSystem guardian death

.gitignore

.idea
myApp.log
target

Application.scala

package akka

import akka.actor._
import com.typesafe.config.{ConfigValueFactory, ConfigFactory, Config}
import scala.collection.JavaConversions._

object Application {

  def main(args: Array[String]): Unit = {

    val system = ActorSystem("test", config)

    println("Wait a bit for everything to settle down")
    Thread.sleep(500)

    println("stuff the logger's mailbox")
    (1 to 10000).foreach { i =>
      system.log.debug("mailbox stuffing " + i)
    }

    println("simulate a failed assertion somewhere in the ActorSystem")
    system.actorOf(Props(new FailingAssertionActor())) ! "message"

    println("Wait a bit for everything to settle down, and things to flush")
    Thread.sleep(500)

    assert(system.isTerminated)
  }

  class FailingAssertionActor
    extends Actor
  {
    override def receive: Receive = {
      case x =>
        assert(false, "it is important that this gets logged")
    }
  }

  val config = {
    System.setProperty("logback.configurationFile", "logback.xml")

    ConfigFactory.load()
      .withValue("akka.loggers", ConfigValueFactory.fromIterable(List("akka.event.slf4j.Slf4jLogger")))
      .withValue("akka.loglevel", ConfigValueFactory.fromAnyRef("DEBUG"))
  }
}

build.sbt

scalaVersion := "2.11.4"

libraryDependencies ++= Seq(
  "com.typesafe.akka" %% "akka-http-experimental" % "1.0-M3",
  "com.typesafe.akka" %% "akka-http-testkit-experimental" % "1.0-M3" % "test",
  "com.typesafe.akka" %% "akka-slf4j" % "2.3.7",
  "ch.qos.logback" % "logback-classic" % "1.1.2")

logback.xml

<configuration>
    <appender name="FILE" class="ch.qos.logback.core.FileAppender">
        <file>myApp.log</file>

        <encoder>
            <pattern>%date %level [%thread] %logger{10} [%file:%line] %msg%n</pattern>
        </encoder>
    </appender>

    <root level="all">
        <appender-ref ref="FILE" />
    </root>
</configuration>