Adding values to an Observable and retrieve them in other js file

I add values to an observable in a function:

var Observable = require('FuseJS/Observable');
var array = Observable('a', 'b', 'c');

// array.add('x');

function add() {

    console.log("array: " + JSON.stringify(array));
module.exports = {
    letters: array,
    add: add

and try to retrieve the values in another js file:

var js1 = require('./js1');

function save() {
    js1.letters.forEach(function(item) {
        console.log("item: " + item);    
module.exports = {
    letters: js1.letters,
    save: save

but only get the first three ones the observable was declared with:

LOG: array: {"_origin":-5,"_subscribers":[],"_isProxy":false,"_values":["a","b","c","z","z","z","z","z"],"_beganSubscriptions":false}
LOG: item: a
LOG: item: b
LOG: item: c

adding something outside of a function ( //array.add(‘x’):wink: everything is fine
Does anybody has an idea why this effect occurs?