So I'm not sure if this is a bug or has something to do with how I coded it but when using a nav group and opening and closing windows, the content of the windows seem to stay when a new window is opened. You can check out my code, however I think it might have something to do with the use of nav.close(win2,{animated: true});, I'm not sure though.

var win2 = Titanium.UI.createWindow({url:'workout.js', navBarHidden: true});
newWorkout.addEventListener('click',function() {
    nav.open(win2,{animated: true});
});

Ti.App.addEventListener('closeWin2', function() {
    nav.close(win2,{animated: true});
});

As you can probably tell I have created a custom back button, so it does not go the normal route.