Type hint problem with scalaz

IDE doesn't help me to decide  type. It thinks that r.subForest returns Any but obviously it returns a Stream[_]. This piece of code compiles fine but IDE give error with message:
Expression of type Any doesn't conform to expected type Stream[_]

import scalaz.Tree

class Foo {
  def foo(r: Tree[Int]) = {
    val xs: Stream[_] = r.subForest
    /*
  package scalaz
  sealed abstract class Tree[A]() extends scala.AnyRef {
    def subForest : scala.Stream[scalaz.Tree[A]]
     */
  }
}

I'm using IDEA 12.1.4 community edition with Sun Java 6 JDK