sandboxed-module error with transitive ES6 deps

bar-es6.js

export default 'bar';

bar.js

module.exports = 'bar';

foo.js

// Does work:
// import bar from './bar';
// Doesn't work:
import bar from './bar-es6';

console.log('foo: bar:', bar);

export default 'foo';

main.js

var traceurAPI = require('traceur/src/node/api.js');
var SandboxedModule = require('sandboxed-module');
var assign = require('lodash-node/modern/objects/assign');

var es6 = function (source) {
    var compiler = new traceurAPI.NodeCompiler({ modules: 'commonjs' });
    return compiler.compile(source);
};

// ES6 modules translate to a CJS module with a default property
var sandboxEs6Require = function (moduleId, options) {
    var defaultOptions = { sourceTransformers: { es6: es6 } };
    return SandboxedModule.require(moduleId, assign({}, defaultOptions, options)).default;
};

var foo = sandboxEs6Require('./foo', { requires: { http: 'mocked http' } });

console.log('main: foo:', foo);

package.json

{
  "name": "sandbox-test",
  "version": "0.0.0",
  "dependencies": {
    "lodash-node": "^2.4.1",
    "sandboxed-module": "^1.0.2"
  },
  "devDependencies": {
    "traceur": "0.0.72"
  }
}