Angular-UI Bootstrap toggle buttons in Angular 1.3

I originally had the default Bootstrap 3.3 toggle buttons in my app. These are the grouping of buttons that mimic the behavior of checkboxes or radio buttons.

I was trying to replace them with the ones here

I paste the code into my html, and at first it looks fine:

  <div class="btn-group">
      <label class="btn btn-default" ng-model="checkModel.left" btn-checkbox>Left</label>
      <label class="btn btn-default" ng-model="checkModel.middle" btn-checkbox>Middle</label>
      <label class="btn btn-default" ng-model="checkModel.right" btn-checkbox>Right</label>
  </div

Now I want to hook up the controller. So, I create a file "elements-buttons.controller.js" with the contents of the JS from the angular-ui site:

(function() {

 'use strict';

 angular.module('pb.ds.elements').controller('ButtonsController', function($log) {
    var _this = this;
   _this.singleModel = 1;
   _this.radioModel = 'Middle';
   _this.checkModel = {
      left: false,
      middle: true,
      right: false
    };
  });
})();

I put the controller into my router:

.state('elements.buttons', {
  url: '/elements/buttons',
  templateUrl: 'modules/elements/templates/elements-buttons.html',
  controller: 'ButtonsController as buttons'
})

Now, as soon as I link the controller to my index.html, the button group loses all styling:

Which makes no sense to me at all. Inspecting the code in Chrome shows it's if fact lost all its classes for some reason:

<div class="btn-group">
      <label class="" ng-model="buttons.checkModel.left" btn-checkbox="">Left</label>
      <label class="" ng-model="buttons.checkModel.middle" btn-checkbox="">Middle</label>
      <label class="" ng-model="buttons.checkModel.right" btn-checkbox="">Right</label>
  </div>

Now, since I have used "controller as" syntax, I did make sure to try adding that to the model ng-model="buttons.checkModel.right" but with or without this same thing. No controller, looks fine. Controller, boom.

EDIT/UPDATE: There are no errors in the console of any kind.