AngularJS Mocking $http returns Error

I am having a bit of trouble testing a HTTP POST in AngularJs with Jasmine.

I have a controller that looks like so:-

appControllers.controller("TaskAddController", function ($scope, $http) {
    $scope.task = {};
    $scope.messages = {};

    $scope.actions = {
        save : function() {
            $http.post("/ajax/tasks/save", $scope.task)
            .then(function() {
                $scope.messages.success = true;
                $scope.task = {};
            });
        }
    };
});

I am testing it like so:-

describe("TaskAddController", function() {
    var createController, scope, $httpBackend;

    beforeEach(function () {
        module('appControllers');

        scope = {};

        inject(function ($injector) {
            $httpBackend = $injector.get("$httpBackend");
        });

        inject(function ($controller) {
            createController = function () {
                return $controller("TaskAddController", { $scope: scope });
            };
        });
    });

    afterEach(function () {
        $httpBackend.verifyNoOutstandingExpectation();
        $httpBackend.verifyNoOutstandingRequest();
    });

    it("when actions.save is called then should call service", function () {
        var task = {
            title: "Title",
            description: "Description"
        };

        $httpBackend.expectPOST("/ajax/tasks/save", task);
        createController();
        scope.task = task;
        scope.actions.save();
        $httpBackend.flush();
    });
});

This causes me to get the following error Error: No pending request to flush !

What am I doing wrong?

Thanks.