Refinement check doesn't dealias

[allanrenucci]

class Test {
  def test = {
    val x: PartialFunction[Int, Int]{ def foo(): Int } = { case x => x } // error:  Lambda does not define foo

    type PF = PartialFunction[Int, Int]{ def foo(): Int }
    val y: PF = { case x => x } // ok
  }
}