Express + Passport + Redis sessions?

To date I have been using the default MemoryStore for my Express sessions. Everything has been working great, except that all session data is lost between restarts. So I am trying to get my sessions working with Redis & Connect-Redis instead.

Here is the part of my code that concerns session config with Redis:

var express = require( "express" ),
    app = module.exports = express(),
    passport = require( "./passport" ),
    http = require( "http" ),
    RedisStore = require( "connect-redis" )( express ),
    redis = require( "redis" ).createClient();

app.configure(function(){

    app.set( "passport", passport );
    app.use( express.cookieParser());
    app.use( express.session({
         secret: "I can haz working sessions?",
         store: new RedisStore({ client: redis })
    }));
    app.use( passport.initialize() );
    app.use( passport.session() );
    ...

When I run this application, there are no errors. However when I try to login, although it performs the initial login, I just keep getting bounced back to the login screen. It is as if passport cannot set a cookie, or cannot read a cookie after it has been set.

For reference, here are the functions I use in passport to serialize / deserialize the session:

passport.serializeUser(function( user, done ) {
    done( null, {
        id : user.id,
        type : user.type,
        firstname: user.firstname,
        lastname: user.lastname
    });
});

passport.deserializeUser(function( user, done ) {
    done( null, user );
});

Any advice on where I am going wrong? Do the passport serializeUser / deserializeUser need to be modified to work with redis? Or am I missing something else?

Thanks (in advance) for your help.