model not updating in .then method of promise angularjs

Question

I'm really struggling with this because it should be very simple. I have a route with a controller defined called login. In my template I have the following data binding {{error}} which is defined in my controller after executing a method from a custom service, and resolving the returned promise.

Controller

app.controller("login", ['$scope','XMLMC', 'ManageSettings', function ($scope,api,ManageSettings) {
    $scope.error = 'test';
    $scope.login = function() {
        var params = {
            selfServiceInstance: "selfservice",
            customerId: $scope.username,
            password: $scope.password
    };
        var authenticated = api.request("session","selfServiceLogon",params).then(function(response) {
            ManageSettings.set("session",response, $scope);

            if(response.status === "ok") {
                window.location.href = 'portal';
            } else {
                $scope.error = response["ERROR"];
                console.log($scope.error);
            }
        });

    };
}]);

The console shows Customer not registered. Showing that $scope.error has been updated appropriately, but the view never gets updated. My service is below, and please note that I am doing nothing "outside" of angular and so I should not have to $apply() anything manually.

app.factory("XMLMC", ['$http', '$q', function ($http, $q) {
    function XMLMC($http, $q) {
        $http.defaults.headers.post['Content-Type'] = 'application/x-www-form-urlencoded; charset=UTF-8';

        var that= this;

        this.prepareForPost = function(pkg) {
            return JSON.stringify(pkg);
        };

        this.request = function(service, request, params, host, newsession) {
            var def = $q.defer();
            var P = def.promise;

            if(request === "analystLogon") {
                newsession = true;
            }

            var call = {
                service: service,
                method: request,
                params: params
            };

            if(host) {
                call.host = host;
            } else {
                call.host = "localhost";
            }

            if(newsession) {
                call.newsession = "true";
            }

            var pkg = {
                contents: this.prepareForPost(call)
            };




            $http.post('php/XMLMC/api.php', jQuery.param(pkg)).success(function (response,status) {
                    that.consume(response, def);

                }).error(function (response,status) {
                    def.reject(response,status);
                });

            return P;


        };

        this.consume = function(response, defer) {
            console.log(response);
            var resp = response[0],
                digested = {},
                i;

            digested.status = resp["attrs"]["STATUS"];
            var params = resp["children"][0]["children"];
            for(i=0; i < params.length; i++) {
                var key = params[i]["name"];
                var val = params[i]["tagData"];
                digested[key] = val;
            }

            defer.resolve(digested);
            //return digested;
        };
    }

    return new XMLMC($http, $q);
}]);

I've created a plunk here with the code exactly as it is on my test server. The routes and etc aren't working for obvious reasons, but you can at least see the code and how it works together

http://plnkr.co/edit/AodFJfCijsp2VWxWpbR8?p=preview

And here is a further simplified plunk where everything has one scope and one controller and no routes. For some reason, this works in the plunk but the $http method fails in my server

http://plnkr.co/edit/nU4drGtpwQwFoBYBfuw8?p=preview

EDIT

Even this fails to update

var authenticated = api.request("session","selfServiceLogon",params).then(function(response) {
            ManageSettings.set("session",response, $scope);

    $scope.error = "foo!";

            if(response.status === "ok") {
                window.location.href = 'portal';
            } 
        });

Answer 1

It appears that $scope.$apply is indeed needed. See AngularJS - why is $apply required to properly resolve a $q promise?

To quote @pkozlowski.opensource:

In AngularJS the results of promise resolution are propagated asynchronously, inside a $digest cycle. So, callbacks registered with then() will only be called upon entering a $digest cycle.