babel error with Set() and spread syntax, when using "loose":true

.babelrc

{
  "presets": [["env", {
      "loose": true
    }
  ]]
}

package.json

{
  "name": "test-babel-set-spread",
  "version": "1.0.0",
  "description": "",
  "scripts": {
    "test:node": "node test-set-spread.js",
    "test:babel": "babel test-set-spread.js | node",
    "build:babel": "babel test-set-spread.js -o test-set-spread.babel.js"
  },
  "license": "ISC",
  "dependencies": {
    "babel-cli": "^6.26.0",
    "babel-preset-env": "^1.6.1"
  }
}

test-set-spread.babel.js

'use strict';

var priorSet = new Set(['a', 'b']);
console.log('prior Set:', priorSet);

var withSpread = new Set([].concat(priorSet, ['e']));
console.log('with spread syntax:', withSpread);

var withArrayFrom = new Set(Array.from(priorSet).concat(['e']));
console.log('with Array.from:', withArrayFrom);

test-set-spread.js

const priorSet = new Set(['a','b']);
console.log('prior Set:', priorSet);

const withSpread = new Set([...priorSet, 'e']);
console.log('with spread syntax:', withSpread);

const withArrayFrom = new Set(Array.from(priorSet).concat(['e']));
console.log('with Array.from:', withArrayFrom);

tests-output.md

$: npm install

$: npm run test:node

prior Set: Set { 'a', 'b' }
with spread syntax: Set { 'a', 'b', 'e' }
with Array.from: Set { 'a', 'b', 'e' }

$: npm run test:babel

prior Set: Set { 'a', 'b' }
with spread syntax: Set { Set { 'a', 'b' }, 'e' }
with Array.from: Set { 'a', 'b', 'e' }

The final line of the code shows an alternative syntax which will pass through babel unharmed, and will work on either end:

const withArrayFrom = new Set(Array.from(priorSet).concat(['e']));