I'm using the fix:

Code:
Ext.data.Model.override({
	    getProxy: function(){
	        return this.self.proxy;
	    }
	});
Code:
	Ext.regModel('User', {
	    fields: [
	        {name: 'firstName', type: 'string'},
	        {name: 'lastName',  type: 'string'},
	        {name: 'age',       type: 'int'},
	        {name: 'eyeColor',  type: 'string'}
	    ],
		proxy: {
			type: 'localstorage',
			id: 'users'
		}
	});

new Ext.data.Store({
		model: 'User',
		storeId: 'UserStore',
		autoLoad: true
	});
	
	var grid = new Ext.grid.GridPanel({
		title: '',
		store: 'UserStore',
		headers: [
			{ text: 'First Name', dataIndex: 'firstName'},
			{ text: 'Last Name', dataIndex: 'lastName'}
		]
	});
		
	var win = new Ext.Window({
		title: 'Webtool List',
		width: 400,
		height: 300,
		layout: 'fit',
		items: [grid],
		buttons: [
			{
				text: 'Add Random',
				handler: function () {
					var user = Ext.ModelMgr.create({
						firstName: 'Bryan',
						lastName: 'Zarzuela',
						age: 29,
						eyeColor: 'Black'
					}, 'User');
					user.save();
				}
			}
		]
	});
	
	win.show();

When I click save for the first time, no error. However, when you reload the page and the store tries to load the data from localStorage, this comes up:

rawData is null
http://ext4test.teleserv.mac:8080/ext/ext-all-debug.js
Line 28519

The previous call from getRecord has a parameter called id with a value of NaN