I think your issue is that all of the windows are using the same store.
What you probably want to do is use a new store for each window, with each store using the same model.
Another approach would be to only allow one window to be open at a time (make the window model when you create it). That way, you can control the store contents on a per window basis.
To make a window modal, in the Controller where you launch the new window, use constrain : true, like this (do not put 'constrain : true' in the View def for this window, put it here, when launching the window):
onChooseNewIpAddress : function (button) {
// Launch the get new ip window.
Ext.create('Portal.view.GetNewIp', {
title : 'Get New IP',
constrain : true
}).show();
}
David