Match Types arguments with bounds do not conform the bounds

[zraffer]

minimized code

sealed trait Off
case class Of[sup, sub <: sup] extends Off
type Sup[O <: Off] = O match { case Of[sup, sub] => sup } // error here!
type Sub[O <: Off] = O match { case Of[sup, sub] => sub } // error here!
type Copy[O <: Off] = Of[Sup[O], Sub[O]]

emits type errors about variables sup, sub do not conform the bounds

expectation

no errors

[s5bug]

Is

sealed trait Foo[A, X <: A]

type FooX[F] = F match {
  case Foo[a, x] => x
}

type MyFoo = Foo[String, "hello"]

val hello: FooX[MyFoo] = "hello"

related? It gives the error:

Found:    ("hello" : String)
Required: FooX[MyFoo]

Even in 3.1.2-RC1.