Missing persist on retaggedInput in RandomForest.run()

  def run(
      input: RDD[LabeledPoint],
      strategy: OldStrategy,
      numTrees: Int,
      featureSubsetStrategy: String,
      seed: Long,
      instr: Option[Instrumentation],
      prune: Boolean = true, // exposed for testing only, real trees are always pruned
      parentUID: Option[String] = None): Array[DecisionTreeModel] = {

    val timer = new TimeTracker()
    timer.start("total")
    timer.start("init")
    val retaggedInput = input.retag(classOf[LabeledPoint]) // it needs to be persisted