Edit in JSFiddle

function MainCtrl($scope) {
  $scope.otherModel = 'b';
}

<div ng-app ng-controller="MainCtrl">
  <div>
    <p>This select gained and selected an empty option because we neglected to assign its model a valid value.</p>
    <select ng-model="someModel">
      <option value="a">A</option>
      <option value="b">B</option>
    </select>
  </div>
  
  <div>
    <p>This select behaves itself because we assigned its model a valid value.</p>
    <select ng-model="otherModel">
      <option value="a">A</option>
      <option value="b">B</option>
    </select>
  </div>
</div>

div+div {
  margin-top: 15px;
}