title: Backbone save triggers 'get' request + urlRoot gets ignored
body: <p>I have the strangest issue ever.  </p>
  
  <p>I instantiate the most basic model:  </p>
  
  <pre><code>define([
    'backbone'
  ], function(Backbone){
  
      //Role - permissions model 
      var Rp_model = Backbone.Model.extend({ 
          urlRoot: '/ingeb/api_v1/users/rolespermissions/'
      }); 
  
      return Rp_model; 
  
  }); 
  </code></pre>
  
  <p>And I save the model like this: </p>
  
  <pre><code>Rolespermissions_controller.prototype.save_userpermission = function(resource_id, role_id, verb){ 
      var rp_model = new Rp_model({'resource_id': 1, 'role_id': 1, 'verb': 'get'}); 
      console.log(rp_model); 
      console.log(rp_model instanceof Backbone.Model); 
      console.log(rp_model.urlRoot); 
      rp_model.save(); 
  }; 
  </code></pre>
  
  <p>The console.logs generate the following output: </p>
  
  <p><img src="https://i.stack.imgur.com/VAG4Z.png" alt="enter image description here"></p>
  
  <p>It doesn't make any sense to me.<br>
  I'm saving the model, and it makes a 'GET' request to the backend.<br>
  Also, it's not clear to me why it ignores the URLRoot completely.  </p>