Switch sometimes (non-deterministically?) results in redundant conditional block

[mediremi]

ReScript version: v12.0.0-alpha.13

The following code (playground link)

type actionType1 =
  | WithoutPayload1
  | WithPayload1({x: int})

type actionType2 =
  | WithoutPayload2
  | WithPayload2({y: int})
  | WithPayload3({y: int})

type actionType3 =
  | WithPayload4({x: int})
  | WithPayload5({y: int})
  | WithPayload6({x: int})
  | WithPayload7({y: int})
  | WithPayload8({x: int})

type action =
  | ...actionType1
  | ...actionType2
  | ...actionType3

let f = (action: action) => {
  switch action {
  | ...actionType3 => Console.log("hello")
  | _ => ()
  }
  42
}

sometimes gets compiled to

function f(action) {
  if (typeof action !== "object") {
    action === "WithoutPayload1";
  } else {
    switch (action.TAG) {
      case "WithPayload1" :
      case "WithPayload2" :
      case "WithPayload3" :
        break;
      default:
        console.log("hello");
    }
  }
  return 42;
}

I say 'sometimes' as by rerunning the compiler you can get the correct output of

function f(action) {
  if (typeof action === "object") {
    switch (action.TAG) {
      case "WithPayload4" :
      case "WithPayload5" :
      case "WithPayload6" :
      case "WithPayload7" :
      case "WithPayload8" :
        console.log("hello");
        break;
    }
  }
  return 42;
}

See this video:

Kooha-2025-05-12-19-47-57.webm