gistfile1.js

var async = require('async');

async.parallel([
    function(callback){
        callback(null, 'one');
    },
    function(callback){
        setTimeout(function() {callback(new Error('ONE'));}, 0);
    },
    function(callback){
        setTimeout(function() {callback(null, 'long');}, 0);
    },
    function(callback){
        callback(null, 'two');
    },
    function(callback){
        callback(new Error('TWO'));
    }
],
// optional callback
function(err, results){
    console.log(err, results);
    // logs              [Error: TWO] [ 'one', , , 'two', undefined ]
    // shouldnt it be:   [Error: TWO] [ 'one', undefined, 'long', 'two', undefined ]
});