Inexhaustive match warning despite being exhaustive

[Swoorup]

Compiler version

3.1.3-RC2

Minimized code

https://scastie.scala-lang.org/oNFJgavuT4ipVnIKcsgUbg

Output

match may not be exhaustive.

It would fail on pattern case: ProjectionState(_1, _2)

Expectation

No warnings expected as match is complete?

[rmgk]

more minimized example

class Projection { type State = String }

sealed trait ProjectionState {
  val a: Projection
  val b: a.State
}

object ProjectionState {
  def apply(first: Projection, second: first.State): ProjectionState =
    new ProjectionState {
      override final val a: first.type = first
      override final val b: second.type = second
    }
  def unapply(pj: ProjectionState): Some[(pj.a.type, pj.b.type)] = Some(pj.a -> pj.b)
}

val projectionStates =
  ProjectionState(Projection(), "string") match {
    case ProjectionState(p, s) => ()
  }