Monix Observable.zip3 bug

BugObservableZip3App.scala

/*
 * Java  1.8.0_162
 * Scala 2.12.4
 * SBT   1.1.0
 * Monix 3.0.0-M3
 */
package satorg.monix_gs

import monix.execution.Scheduler.Implicits.global
import monix.reactive._

import scala.concurrent._
import scala.concurrent.duration._

object BugObservableZip3App extends App {

  val ob1 = Observable.fromIterable(1 to 3).map { x => println(s"ob1: $x"); x }
  val ob2 = Observable.fromIterable(1 to 4).map { x => println(s"ob2: $x"); x }
  val ob3 = Observable.fromIterable(1 to 5).map { x => println(s"ob3: $x"); x }

  println("\nEXAMPLE1:")
  Await.result(Observable.zip2(ob1, ob2).foreach(xx => println(s"res: $xx")), Duration.Inf)
  // example1 works...

  println("\nEXAMPLE2:")
  Await.result(Observable.zip2(ob2, ob3).foreach(xx => println(s"res: $xx")), Duration.Inf)
  // example2 works as well...

  println("\nEXAMPLE3:")
  Await.result(Observable.zip3(ob1, ob2, ob3).foreach(xx => println(s"res: $xx")), Duration.Inf)
  // example3 either hangs or fails with the exception:
  //
  // java.lang.IllegalStateException: Promise already completed.
  //   at scala.concurrent.Promise.complete(Promise.scala:49)
  //   at scala.concurrent.Promise.complete$(Promise.scala:48)
  //   at scala.concurrent.impl.Promise$DefaultPromise.complete(Promise.scala:183)
  //   at scala.concurrent.Promise.success(Promise.scala:82)
  //   at scala.concurrent.Promise.success$(Promise.scala:82)
  //   at scala.concurrent.impl.Promise$DefaultPromise.success(Promise.scala:183)
  //   at monix.reactive.internal.builders.Zip3Observable.monix$reactive$internal$builders$Zip3Observable$$signalOnComplete$1(Zip3Observable.scala:133)
  //   at monix.reactive.internal.builders.Zip3Observable$$anon$2.onComplete(Zip3Observable.scala:183)
  //   at monix.reactive.internal.operators.MapOperator$$anon$1.onComplete(MapOperator.scala:61)
  //   at monix.reactive.internal.builders.IteratorAsObservable.fastLoop(IteratorAsObservable.scala:176)
  //   at monix.reactive.internal.builders.IteratorAsObservable.$anonfun$reschedule$1(IteratorAsObservable.scala:109)
  //   at monix.reactive.internal.builders.IteratorAsObservable.$anonfun$reschedule$1$adapted(IteratorAsObservable.scala:104)
  //   at scala.concurrent.impl.CallbackRunnable.run(Promise.scala:60)
  //   at scala.concurrent.impl.ExecutionContextImpl$AdaptedForkJoinTask.exec(ExecutionContextImpl.scala:140)
  //   ...

  println("DONE") // never is printed :)
}