Why does Express look for static files in wrong location when url path is more than two levels deep?

The Express version is the latest.

This is the app.js file, which is used by another app.js file:

"use strict";
var express = require('express'), engine = require('ejs-locals');
var path = require('path'), map = require('../../app').map;
var register = require('./routes/register').register;   
var profile = require('./routes/profile').profile;      
var login = require('./routes/login').login;            

var app = module.exports = express();
app.configure(function() {
    app.engine('ejs', engine);
    app.set('views', __dirname + '/views');
    app.set('view engine', 'ejs');
    app.use('/assets', express.static(path.join(__dirname, 'assets')));
});

app.configure('development', function() {
    app.use(express.errorHandler());
});

app.map = map;
app.map(app, {
    '/seller': {
        '/password': {
            get: login.forgot, // Looks in the correct place /assets/css/... etc.
            '/forgot': {
                get: login.forgot // Looks in wrong place /seller/assets/... etc.
            },
            '/reset': {
                get: login.reset
            }
        }
    }
});

When GET http://localhost:3000/seller/password is requested, Express looks for the static files in the correct location, namely /assets/css/.

But when GET http://localhost:3000/seller/password/forgot is requested, Express looks for the static files in the wrong place, namely /seller/assets/css, which does not even exist.

This is the map function. It is taken from the Express route-map example.

function route_map(app, a, route) {
    route = route || '';
    for (var key in a) {
        switch (typeof a[key]) {
            case 'object': // { '/path': { ... }}
            app.map(app, a[key], route + key);
            break;
            case 'function': // get: function(){ ... }
            app[key](route, a[key]);
            break;
        }
    }
}