AngularJS service parent separate reference

I'm using an AngularJS service to store data from multiple pages, to be submitted together. See the code below.

In my Chrome console if I observe checkoutData.shipping, I get back the correct object with data. If I observe checkoutData.data I get an empty object, where it's shipping property is blank.

These should be pointing at the same object, right? Why would it work with .shipping and not using .data? The reason it's set up this way is that the shipping page only cares about .shipping, while the final page needs everything in .data.

(function() {
    angular.module('app').factory('checkoutData', [function() {
        var data = {
            carrierId: null,
            serviceTypeId: null,
            shippingCost: {},
            billingOptionId: null,
            shipping: {},
            billing: {},
            cart: null
        };
        var inputForms = {};
        var options = {
            shippingOptions: null,
            billingOptions: null,
            selectedShippingOption: null
        };
        var staticContent = {
            billing: {},
            cart: {},
            shipping: {}
        };
        return {
            data: data,
            shipping: data.shipping,
            inputForms: inputForms,
            cart: data.cart,
            billingOptionId: data.billingOptionId,
            billingOptions: options.billingOptions,
            carrierId: data.carrierId,
            serviceTypeId: data.serviceTypeId,
            shippingOptions: options.shippingOptions,
            staticContentBilling: staticContent.billing,
            staticContentCart: staticContent.cart,
            staticContentShipping: staticContent.shipping,
            selectedShippingOption: options.selectedShippingOption,
            setValid: function(formName, valid) {
                inputForms[formName].valid = valid;
            },
            initializeForm: function(formName) {
                inputForms[formName] = {};
            },
            formInitialized: function (formName) {
                return inputForms[formName] != null;
            }
        }
    }]);
})();

via Chebli Mohamed