angularjs factory $http multiple methods return same dataset

I have a factory with 4 methods but when i call any of them i always get the dataset returned from the first method called.

Factory code:

app.factory('EnumLookupsSvc', function ($http) {
var factory = {};

var promise;

factory.getInvoiceTypes = function() {
    if (!promise) {
        // $http returns a promise, which has a then function, which also returns a promise
        promise = $http.get('/api/invoice/GetInvoiceTypes').then(function(response) {
            // The then function here is an opportunity to modify the response
            console.log(response);
            // The return value gets picked up by the then in the controller.
            return response.data;
        });
    }
    // Return the promise to the controller
    return promise;
};

    factory.getLtlClasses = function() {
        if (!promise) {
            // $http returns a promise, which has a then function, which also returns a promise
            promise = $http.get('/api/invoice/GetLtlClasses').then(function(response) {
                // The then function here is an opportunity to modify the response
                console.log(response);
                // The return value gets picked up by the then in the controller.
                return response.data;
            });
        }
        // Return the promise to the controller
        return promise;
    };

    factory.getDirections = function() {
        if (!promise) {
            // $http returns a promise, which has a then function, which also returns a promise
            promise = $http.get('/api/invoice/GetDirections').then(function(response) {
                // The then function here is an opportunity to modify the response
                console.log(response);
                // The return value gets picked up by the then in the controller.
                return response.data;
            });
        }
        // Return the promise to the controller
        return promise;
    };

    factory.getLineItemTypes = function() {
        if (!promise) {
            // $http returns a promise, which has a then function, which also returns a promise
            promise = $http.get('/api/invoice/GetLineItemTypes').then(function(response) {
                // The then function here is an opportunity to modify the response
                console.log(response);
                // The return value gets picked up by the then in the controller.
                return response.data;
            });
        }
        // Return the promise to the controller
        return promise;
    };


return factory;
});

Controller Code:

"use strict";

app.controller('InvoiceDetailEditorCtrl', function ($scope, $routeParams, InvoiceSvc, EnumLookupsSvc) {

EnumLookupsSvc.getLtlClasses().then(function (data) {
    $scope.ltlClasses = data;
});

EnumLookupsSvc.getDirections().then(function (data) {
    $scope.directions = data;
});

EnumLookupsSvc.getLineItemTypes().then(function (data) {
    $scope.lineItemTypes = data;
});

EnumLookupsSvc.getInvoiceTypes().then(function (data) {
    $scope.invoiceTypes = data;
});

$scope.invoice = InvoiceSvc.get({ id: $routeParams.invoiceId });



});

Chromes network monitor shows only one request is made to /api/invoice/GetLtlClasses

FIXED! *The fix was to move the var promise into the methods:*

factory.getInvoiceTypes = function () {
    var promise;
    if (!promise) {
        // $http returns a promise, which has a then function, which also returns a promise
        promise = $http.get('/api/invoice/GetInvoiceTypes').then(function(response) {
            // The then function here is an opportunity to modify the response
            console.log(response);
            // The return value gets picked up by the then in the controller.
            return response.data;
        });
    }
    // Return the promise to the controller
    return promise;
};