Can't use Handlebars to generate class name

I'm using Ember.js with a Rails app, but when I want to dynamically change class name depending on the data, I get an error. Here is the Handlebars file:

<ul id="data-all" class="list-items">
  {{#each datum in data}}
    <li class="list-item">
      {{#link-to 'data.datum' datum.name classNames="link-item"}}
        <span class="datum-last-action datum-{{datum.name}}">{{datum.name}}</span>
      {{/link-to}}
    </li>
  {{/each}}
</ul>

And the generated errors:

Uncaught Error: Assertion Failed: An error occured while setting up template bindings. Please check for invalid markup or bindings within HTML comments.
Uncaught Error: Something you did caused a view to re-render after it rendered but before it was inserted into the DOM.

All the doc I found don't give special warning using this, so why does this occure?

Thanks