title: angularjs watching radio button for change working only at first selections
body: <p>So I have a list of radio buttons and I am trying to watch the change of selection with $watch in a directive. I am only able to trigger the watch at the first selection of those elements.</p>
  
  <p>My html:</p>
  
  <pre><code>&lt;p ng-repeat="(key,item) in option" style="margin-bottom:0px "&gt;
      &lt;label&gt;
          &lt;input type="radio" is-valid ng-model="value" selected-key="value" name="select" value="{{key}}" ng-checked="getChecked($index)"&gt; {{item.name}}
      &lt;/label&gt;
  &lt;/p&gt;
  </code></pre>
  
  <p>My Directive returns:</p>
  
  <pre><code>return {
      restrict: "A",
      scope: {
          selectedKey: '='
      },
      link: function(scope, elem, attrs) {
          scope.$watch('selectedKey', function(newValue, oldValue, scope) {
              alert('triggered')
          });
      }
  }
  </code></pre>
  
  <p>What am I doing wrong? I tried watching with "value" only but watch doesnot get triggered.</p>
  
  <p>Thank you in advance  </p>