Explicit type for a record loses Witness.Aux about shapeless HOT 4 CLOSED

object TestExplicitRecordType {
  import shapeless._, labelled._, record._, syntax.singleton._

  object testF extends Poly1 {
    implicit def atFieldType[F, V](implicit wk: shapeless.Witness.Aux[F]) = at[FieldType[F, V]] {
      f => wk.value.toString
    }
  }

  type Error = Record.`"k1" -> String, "k2" -> Long`.T

  // That seems to work...
  val err1        = "k1" ->> "1" :: "k2" ->> 1L :: HNil
  val err2: Error = "k1" ->> "1" :: "k2" ->> 1L :: HNil

  testF(err1.head)  // OK
  testF(err2.head)  // OK
}