Spurious "Unreachable case" warning

[odersky]

Compiler version

3.1.1-RC1

Minimized example

trait T[-X]
case class CC[-X](x: List[T[X]]) extends T[Nothing]
case class Id[-X](x: String) extends T[X]

def f[X](tree: T[X]) = tree match
  case CC(Id("hi") :: Nil) => ???
  case CC(refs) => ???
  case _ => ???

Output

-- [E030] Match case Unreachable Warning: ../../new/test.scala:8:7 -------------
8 |  case CC(refs) => ???
  |       ^^^^^^^^
  |       Unreachable case
1 warning found

Expectation

No warning