title: Backbone model.save() not calling either error or success callbacks
body: <p>I'm trying to update a record in DB so I'm defining model with data and calling .save() method. The PUT request is triggered and the database entry is updated. The problem is neither success or error callbacks are called. What could be the cause?</p>
  
  <pre><code>sessionsModel.save({
      error: function() {
          alert('test');
      },
      success: function () {
          alert('test');
      }
  });
  </code></pre>
  
  <p>Edit: Request returns JSON object</p>