Bug with dependent types in scala 2.10

bug.scala

trait Path {
  type A
}

trait Reader { self =>
  def read(p: Path): Option[p.A]

  def orElse(that: Reader): Reader = ComposedReader(this, that)
}

case class ComposedReader(first: Reader, second: Reader) extends Reader {
  // this works
  def read(p: Path): Option[p.A] = first.read(p).orElse(second.read(p))
  /* this gives the error below
  def read(p: Path) = first.read(p).orElse(second.read(p))
  */
}

/**
 * This gives me a confusing message in scala 2.10.4:
[tw-mbp-oscar deptype-bug]$ scalac test.scala 
test.scala:9: error: type mismatch;
 found   : Option[p.A]
 required: Option[p.A]
    def read(p: Path) = self.read(p).orElse(that.read(p))
*/