`export default` bloats exported object

`export default` does not work as expected 

``` js
// test.js
let Test = {
  test() { return 'ok' }
}

export default Test
export let test = () => 'ko'
```

``` js
// main.js
import Test from './test'
import assert from 'assert'

assert.equal(Test.test(), 'ok') // AssertionError: "ko" == "ok"
```
