How to correctly pipeline Node.js duplex streams?

Question

I have multiple duplex streams with asynchronous flush methods, but pipeline does wait for only one of them.

Working example code:

const { pipeline, Readable, PassThrough, Writable } = require('stream')
const { promisify } = require('util')

const wait = (ms) => {
  return new Promise((resolve) => setTimeout(resolve, ms))
}

// Send X items and close
// * -> 0, 1, 2, ..
const s1 = new Readable({
  read() {
    new Array(20)
      .fill(0)
      .map((_, i) => i)
      .map(String)
      .forEach(item => {
        this.push(item)
      })
    this.push(null)
  }
})

// Pass through all items
// On flush, wait a bit and emit an additional data at the end of the stream.
const s2 = new PassThrough({
  async flush(cb) {
    console.log('S2 Thinking')
    await wait(2000)
    this.push('s2')
    console.log('S2 Done')
    cb()
  }
})

// Techincally the same as s2
const s3 = new PassThrough({
  async flush(cb) {
    console.log('S3 Thinking')
    await wait(1000)
    this.push('s3')
    console.log('S3 Done')
    cb()
  }
})

const main = async() => {
  // Wait until the pipeline is finished
  await promisify(pipeline)(s1, s2, s3)
  console.log('pipeline done')
}

main()
  .catch(error => {
    console.error(`CRITICAL FAILURE`)
    console.error(error.stack)
  })

Why pipeline resolves when s2 is done, but does not wait for s3? Am I misusing the pipeline?

Output of this is

S2 Thinking
S2 Done
S3 Thinking
pipeline done
S3 Done

But I expect it to be

S2 Thinking
S2 Done
S3 Thinking
S3 Done
pipeline done