mixed done and promise in lab leads to confusing warning

package.json

{
  "name": "some-lab-test",
  "version": "1.0.0",
  "description": "",
  "main": "index.js",
  "scripts": {
    "test": "lab --verbose --debug"
  },
  "keywords": [],
  "author": "",
  "license": "ISC",
  "devDependencies": {
    "lab": "10.5.1"
  }
}

test_slash_index.js

'use strict'

const Lab = require('lab');
const lab = exports.lab = Lab.script();

const describe = lab.describe;
const it = lab.it;

describe('my test suite', function() {
    
    /*
    This gives the following error at the end of the test suite:
    
    Test script errors:

        Multiple callbacks or thrown errors received in test "my test suite should give me a better warning" (undefined)
        
    */
    it('should give me a better warning', function(done) {
        return new Promise(function(resolve) {
            setTimeout(function() {
                resolve('we are done here')
            }, 1000)
        })
        .then(function() {
            done()
        })
    })
})