native required radio button is always invalid

[jimmywarting]

Steps to reproduce

1. Create a form with a required radio button

<form>
  <md-radio name="foo" required v-model="radio">foo</md-radio>
  <md-button type="submit">submit</md-button>
</form>

2. select (check) the radio button
3. submit

What is expected?

the form should be submitted

What is actually happening?

Nothing! I'm using the constraint validation and the form is still invalid, since the actual radio button is never checked. Only the model value is synced not the checked state on the actual <input type="radio">.