@mswjs/http-middleware behavior mismatch between createServer and createMiddleware

curl.sh

$ curl -X POST -d '{"foo":"bar"}' -H "Content-Type: application/json" http://localhost:9090/user
{"firstName":"John"}

middleware.js

import { createMiddleware } from "@mswjs/http-middleware";
import express from "express";
import { rest } from "msw";

const handlers = [
  rest.post("/user", (req, res, ctx) => {
    console.log(req.body);
    return res(ctx.json({ firstName: "John" }));
  }),
];

const app = express();
// app.use(express.json()); // this seems to be required to get data to the handlers?
app.use(createMiddleware(...handlers));
app.listen(9090, () => {
  console.log("Server available");
});

package.json

{
  "name": "msw-test",
  "version": "1.0.0",
  "description": "",
  "main": "index.js",
  "scripts": {
    "test": "echo \"Error: no test specified\" && exit 1"
  },
  "author": "",
  "license": "ISC",
  "devDependencies": {
    "@mswjs/http-middleware": "^0.3.0",
    "express": "^4.17.3",
    "msw": "^0.39.2"
  },
  "type": "module"
}

server.js

import { createServer } from "@mswjs/http-middleware";
import { rest } from "msw";

const handlers = [
  rest.post("/user", (req, res, ctx) => {
    console.log(req.body);
    return res(ctx.json({ firstName: "John" }));
  }),
];

const app = createServer(...handlers);
app.listen(9090);

test.sh

$ node middleware.js
Server available
undefined
^C

$ node server.js
{ foo: 'bar' }