Bind-attr "for" attribute in Ember.js

I'm trying to include a unique id for an and tag to get a custom checkbox. The {{input}} tag outputs it correctly but the <label {{bind-attr for=binding}} does not. I'm a frontend guy new to Ember so I'm sure this should be trivial.

<ul class="col-menu dropdown-menu">
  {{#each columns}}
    <li>
      {{input type="checkbox" checked=checked id=binding}} 
      <label {{bind-attr for=binding}}><span></span></label>
      <span>{{heading}}</span>
      {{columns}}
    </li>
  {{/each}}
</ul>

Here is the output ...

<li>
  <input id="activityTotal" class="ember-view ember-checkbox" type="checkbox" checked="checked"> 
  <label data-bindattr-2689="2689">
    <span></span>
  </label>
  <span>
    <script id="metamorph-53-start" type="text/x-placeholder"></script>
    Events
    <script id="metamorph-53-end" type="text/x-placeholder"></script>
  </span>
  <script id="metamorph-54-start" type="text/x-placeholder"></script>
  <script id="metamorph-54-end" type="text/x-placeholder"></script>