vm: references to context inside objects are not === the original context

Failing test case:

var common = require('../common');
var assert = require('assert');
var vm = require('vm');

var sandbox = {};
sandbox.document = { defaultView: sandbox };

vm.createContext(sandbox);

vm.runInContext('var result = document.defaultView === this', sandbox);

assert.equal(sandbox.result, true);

Investigating this in my local build ... this is the only remaining test suite failure after switching jsdom to io.js vm.