webdriver parallel executeAsync bug

executeAsync.js

import {expect} from 'chai'
import * as webdriverio from 'webdriverio'
import {run as runPhantomjs} from 'phantomjs-prebuilt'

describe('executeAsync', function () {
  this.timeout(10000)

  let phantomjs
  let browser

  before(async function () {
    phantomjs = await runPhantomjs('--webdriver=4444')
    browser = webdriverio.remote({
      desiredCapabilities: {browserName: 'phantomjs'},
      logLevel: 'verbose'
    })
    await browser.init()
  })
  after(async function () {
    if (browser) await browser.end()
    if (phantomjs) phantomjs.kill()
  })

  it("parallel calls don't interfere with each other", () => Promise.all([
    browser.executeAsync(
      (count, callback) => setTimeout(() => callback(count), 2000),
      1
    ).then(({value: count}) => expect(count).to.equal(1)),
    browser.executeAsync(
      (count, callback) => setTimeout(() => callback(count), 2000),
      2
    ).then(({value: count}) => expect(count).to.equal(2)),
  ]))
})

log.txt

  executeAsync

=======================================================================================
Selenium 2.0 / webdriver protocol bindings implementation with helper commands in nodejs.
For a complete list of commands, visit http://webdriver.io/api.html.
=======================================================================================

[16:52:17]  COMMAND	POST 	 "/wd/hub/session"
[16:52:17]  DATA		{"desiredCapabilities":{"javascriptEnabled":true,"locationContextEnabled":true,"handlesAlerts":true,"rotatable":true,"browserName":"phantomjs","loggingPrefs":{"browser":"ALL","driver":"ALL"},"requestOrigins":{"url":"http://webdriver.io","version":"4.6.2","name":"webdriverio"}}}
[16:52:17]  INFO	SET SESSION ID 4a3e0890-2481-11e7-94ca-3f5238c619af
[16:52:17]  RESULT		{"browserName":"phantomjs","version":"2.1.1","driverName":"ghostdriver","driverVersion":"1.2.0","platform":"mac-unknown-64bit","javascriptEnabled":true,"takesScreenshot":true,"handlesAlerts":false,"databaseEnabled":false,"locationContextEnabled":false,"applicationCacheEnabled":false,"browserConnectionEnabled":false,"cssSelectorsEnabled":true,"webStorageEnabled":false,"rotatable":false,"acceptSslCerts":false,"nativeEvents":true,"proxy":{"proxyType":"direct"}}
[16:52:17]  COMMAND	POST 	 "/wd/hub/session/4a3e0890-2481-11e7-94ca-3f5238c619af/execute_async"
[16:52:17]  DATA		{"script":"return (function (count, callback) {\n      return setTimeout(function () {\n        return callback(count);\n      }, 2000);\n    }).apply(null, arguments)","args":[1]}
[16:52:17]  COMMAND	POST 	 "/wd/hub/session/4a3e0890-2481-11e7-94ca-3f5238c619af/execute_async"
[16:52:17]  DATA		{"script":"return (function (count, callback) {\n      return setTimeout(function () {\n        return callback(count);\n      }, 2000);\n    }).apply(null, arguments)","args":[2]}
[16:52:19]  RESULT		1
    1) can be run in parallel without issues
[16:52:19]  RESULT		1
[16:52:19]  COMMAND	DELETE 	 "/wd/hub/session/4a3e0890-2481-11e7-94ca-3f5238c619af"
[16:52:19]  DATA		{}
[16:52:19]  RESULT		{}


  0 passing (3s)
  1 failing

  1) executeAsync can be run in parallel without issues:

      AssertionError: expected 1 to equal 2
      + expected - actual

      -1
      +2
      
      at Object.<anonymous> (test/executeAsync.js:32:49)
      at Object.exec (node_modules/webdriverio/build/lib/helpers/safeExecute.js:28:24)
      at Object.resolve (node_modules/webdriverio/build/lib/webdriverio.js:193:29)
      at node_modules/webdriverio/build/lib/webdriverio.js:503:32
      at _fulfilled (node_modules/q/q.js:834:54)
      at self.promiseDispatch.done (node_modules/q/q.js:863:30)
      at Promise.promise.promiseDispatch (node_modules/q/q.js:796:13)
      at node_modules/q/q.js:604:44
      at runSingle (node_modules/q/q.js:137:13)
      at flush (node_modules/q/q.js:125:13)
      at _combinedTickCallback (internal/process/next_tick.js:67:7)
      at process._tickDomainCallback (internal/process/next_tick.js:122:9)