AngularJS Radio group not setting $dirty on field - html

Question

I'm trying to use Angular's $dirty flag to submit only the changed fields in a form.
When I ran into radio button groups, I was missing the changes in the list of changed fields. I have a fiddle that reproduces the problem I am seeing.
<div ng-app="form-example" ng-controller="MainCtrl">
<form name="form" novalidate>
<input type="radio" name="myRadio" ng-model="myRadio" value="one" required>One<br />
<input type="radio" name="myRadio" ng-model="myRadio" value="two" required>Two<br />
<input type="radio" name="myRadio" ng-model="myRadio" value="three" required>Three<br />
<input type="radio" name="myRadio" ng-model="myRadio" value="four" required>Four<br />
<input type="radio" name="myRadio" ng-model="myRadio" value="five" required>Five<br /><br />
Form $dirty: {{form.$dirty}}<br />
Field $dirty: {{form.myRadio.$dirty}}<br />
Value: {{myRadio}}
</form>
</div>
The field's $dirty flag will only change when the last radio button is clicked even though the form $dirty updates properly.
Am I missing something fundamental here? and is there a workaround for this behavior?

Answer 1

Each ng-model actually instantiates a controller.
When you click any radio button, the controller sets $dirty field to true and sets form.$dirty to true.
The problem is that form.myRadio holds the reference to the last radio button's model.
As a workaround you can use nested forms with ng-form. See here: http://jsfiddle.net/UM578/

Answer 2

I gave each radio input a unique name. Maybe you can give a broader view of what you are trying to do.
<div ng-app="form-example" ng-controller="MainCtrl">
<form name="form" novalidate>
<input type="radio" name="myRadio1" ng-model="myRadio" value="one" required>One<br />
<input type="radio" name="myRadio2" ng-model="myRadio" value="two" required>Two<br />
<input type="radio" name="myRadio3" ng-model="myRadio" value="three" required>Three<br />
<input type="radio" name="myRadio4" ng-model="myRadio" value="four" required>Four<br />
<input type="radio" name="myRadio5" ng-model="myRadio" value="five" required>Five<br /><br />
Form $dirty: {{form.$dirty}}<br />
Field 1 $dirty: {{form.myRadio1.$dirty}}<br />
Field 2 $dirty: {{form.myRadio2.$dirty}}<br />
Field 3 $dirty: {{form.myRadio3.$dirty}}<br />
Field 4 $dirty: {{form.myRadio4.$dirty}}<br />
Field 5 $dirty: {{form.myRadio5.$dirty}}<br />
Value: {{myRadio}}
</form>