title: AngularJS service not invoking error callback on save() method
body: <p>So I'm using angularjs restful service $resource and I'm calling $save function.  However, the error callback I pass to it is not being called.  The server is sending a 418 error which I thought since it's NOT 200 would result in the error callback being invoked.  But, it never does.  I can't find any documentation stating what http error codes will result in the error callback being called. </p>
  
  <p>Here is my code:</p>
  
  <pre><code>var modalScope = $scope.$new();
  modalScope.showPassword = false;
  modalScope.message = null;
  modalScope.user = new User();
  
  modalScope.submit = function(user) {
      user.$save( {}, function(data,headers) {
          // do the success case
      }, function(data,headers) {
          // do the error case                
      });
  };
  </code></pre>
  
  <p>The modalScope.user is being passed to the submit function defined.  So what's the problem why this error callback isn't being called? </p>