CodeIgniter REST API调用不存在的方法

Using Phil Sturgeon's Codeigniter REST SERVER, I've set up a basic REST server to interact with a Backbone application. The issue is that whenever the applcation tries to make a DELETE request to the proper URI (for instance, api/object/7 where 7 is the ID number in question), REST returns a 404 Not Found error. A bit of digging revealed that it was trying to reach the nonexistint 7_delete within the controller instead of calling index_delete as it should.

I've checked the requests, and they're routing to the correct URL; I've also checked that there are no custom routes set up which would interfere and there are none. Suggestions?

EDIT: For more detail, the Backbone routing is set up like this:

urlRoot: 'api/objective/',

The Objective controller in CI meanwhile is set up like this:

class Objective extends REST_Controller {

  /**
   *  Respond to a POST request;
   *  - If given an ID, update an existing record
   *  - If given no ID, create a new record
   */
  public function index_post() {
    // code here...
  }

  /**
   *  Delete an existing record from a passed URL
   */
  public function index_delete($id) {
    // Code here...
  }

  /**
   *  Get a single record
   */
  public function index_get($id) {
    // Code here...
  }

  /**
   *  Get the full objectives list
   */
  public function index_get() {
    // Code here...
  }
}

This is close to the example provided in the original example file. The CI routing has nothing set up however.

maybe it easy when you use url like this http://example.com/api/objective/deletecontent/id/7

    public function deletecontent_get() {
        if(!$this->get('id')) {$this->response(null,400)}
          $run = $this->some_model->delete_content_by_id($this->get('id));
          if($run) $this->response(true,200);
          else $this->response(null,304);
    }