角度选择始终标记为无效 - 必需指令已损坏

Question

出于某种原因，无论选择哪个选项，一旦触摸该字段，该字段始终被标记为无效。

HTML：

<md-input-container class="md-block">
    <label>Select</label>
    <md-select flex
               id="mySelect"
               ng-model="myModel.mySelect"
               ng-change="myCallback()"
               placeholder="Select"
               required>
        <md-option ng-repeat="option in options | orderBy:'option.name'"
                   ng-value="option.id">
            {{option.name}}
        </md-option>
    </md-select>
</md-input-container>

控制器：

.controller( 'myController', function ( $scope, $mdDialog, myModel ) {

  $scope.options = [{name: "option1", id:1},{name:"option2", id:2},{name: "option3", id:3}];
  $scope.isModified = false;

  $scope.myModel = angular.copy(myModel);

  $scope.save = function ( model ) {
    $mdDialog.hide( angular.copy( model ) );
  };


  $scope.myCallback = () => $scope.isModified = !angular.equals(myModel, $scope.myModel);
})