Limited type inference when using Any

[jiribenes]

effect throw[A](x: A): Nothing

def f[A]() = {
  def left(x: A): Unit / throw[A] = do throw(x)
  def right { f: => Unit / throw[A] } =
    try { f(); None() } with throw[A] { x => Some(x) }

  (box left, box right)
}

def upcast[A](x: A): Any = x
def main(): Unit = {
  def block(): Unit / throw[Any] = (unbox f[Any]().first)(42.upcast)

  val r = (unbox f[Any].second) { () => block() }
  //                            ^^^^^^^^^^^^^^^^^
  // Effects need to be fully known, but effect throw[A]'s type parameter(s) A could not be inferred. Maybe try annotating them?
  inspect(r)
}

When I try to be more specific:

def apply { g: => Unit / throw[Any] } = (unbox f[Any].second) {g}
// Cannot fully infer type for apply: {() => Unit / { throw[Any] }} => Option[A]

This error is especially weird, do we not propagate the result of the substitution somewhere?
I have to ascribe the Option[Any] return type here for it to work...

Only then the program starts working (here's the playground link)