Issue during Angular validating form with two radio buttons - angularjs

Question

Today I approached a weird case: I got form with two radio buttons.
When one, currently checked, is disabled, form shouldn't be able to submit.
The thing is, that standard way with form.$valid doesn't work :-/
UPDATE
Even if I watch for changes in form, $invalid status is not reflected on ng-disable save button. Why?
<input name="someRadio" ng-disabled="true" type="radio" value="CURRENT" ng-model="RadioPen.data.radio" required>
<input name="someRadio" type="radio" value="DELAYED" ng-model="RadioPen.data.radio" required>
<button ng-disabled="!RadioPen.someForm.$valid">Save</button>
Here is full working example: CodePen

Answer 1

The form.$valid is working fine. The required check works based on the value of a form element. Since you are already providing a value to the model associated with the radio buttons, i.e, RadioPen.data.radio, in your controller script, the required condition is being fulfilled and hence the form is getting validated. Here is a modified and working version of your code where I have removed the initialization of the model for the radio buttons.
angular
.module('test', [])
.controller('RadioPen', radioPen)
function radioPen($scope) {
var vm = this;
vm.data= {};
$scope.RadioPen = vm;
}
<script src="https://ajax.googleapis.com/ajax/libs/angularjs/1.2.23/angular.min.js"></script>
<div ng-app="test">
<form name="RadioPen.someForm" ng-controller="RadioPen" novalidate>
Current
<input name="someRadio" ng-disabled="true" type="radio" value="CURRENT" ng-model="RadioPen.data.radio" required>
Delayed
<input name="someRadio" type="radio" value="DELAYED" ng-model="RadioPen.data.radio" required>
<button ng-disabled="!RadioPen.someForm.$valid">Save</button>
{{'is valid: ' + RadioPen.someForm.$valid}}
</form>
</div>

Answer 2

check this out:
<div ng-app="test">
<form name="ctrl.someForm" ng-controller="RadioPen as ctrl" novalidate>
Current
<input name="someRadio" ng-disabled="true" type="radio" value="CURRENT" ng-model="RadioPen.data.radio" required>
Delayed
<input name="someRadio" type="radio" value="DELAYED" ng-model="RadioPen.data.radio" required>
<button ng-disabled="ctrl.someForm.$invalid">Save</button>
{{'is invalid: ' + ctrl.someForm.$invalid}}
</form>
</div>