Why would events be published more than once?

gistfile1.txt

var Config = require('../config.js').Config;
var eventstore = require('eventstore');
var storage = require('eventstore.mongodb');

var es;

var S4 = function() {
    return Math.floor((1 + Math.random()) * 0x10000).toString(16).substring(1);
};

var guid = function() {
    return (S4()+S4()+"-"+S4()+"-"+S4()+"-"+S4()+"-"+S4()+S4()+S4());    
}

var publisher = {
    publish : function(event) {
        console.log(event);
    }
};

module.exports = {

    setUp: function (callback) {         

        es = eventstore.createStore();

        storage.createStorage({ host: 'localhost', port: 27017, dbName: 'eventstore', eventsCollectionName: 'events', snapshotsCollectionName: 'snapshots' }, function(err, store) {
            es.configure(function() {
                es.use(store);             
                es.use(publisher);
            });
            
            es.start(callback);
        });

    },

    tearDown: function (callback) {                     
        callback();
    },  

    when_creating_a_stream_it_is_created: function (test) {       
       
        var id = guid();

        es.getEventStream(id, function(err, stream) {
            if (err) throw err;         

            stream.addEvent({ 'name' : 'account_debited', 'accountNumber' : 'XXXAAA', 'timestamp' : new Date() });
            stream.commit(function() {               
                es.getEventStream(id, 0, -1, function(err, stream) {                    
                    if (err) throw err;         

                    test.equal(stream.events.length, 1);
                    test.done();            
                });
            });           
        });
       
    },

/*    when_adding_an_event_to_an_existing_stream_it_is_added: function (test) {       

        var id = guid();

        es.getEventStream(id, function(err, stream) {
            if (err) throw err;         

            stream.addEvent({ 'name' : 'account_debited', 'accountNumber' : 'XXXAAA', 'timestamp' : new Date() });
            stream.commit(function() {
                 
                es.getEventStream(id, function(err, stream) {
                    if (err) throw err;         

                    stream.addEvent({ 'name' : 'account_credited', 'accountNumber' : 'XXXAAAA', 'timestamp' : new Date() });
                    stream.commit(function() {

                        es.getEventStream(id, 0, -1, function(err, stream) {    
                            if (err) throw err;         

                            test.equal(stream.events.length, 2);
                            test.done();            
                        });

                    });
                });
                
            });           
        });
       
    }, */

};

can you try with the inMemory db or with

var es = eventstore.createStore({
forkDispatching: true
});