@kelltic,
You should double check that when you change the theme settings, the theme software or settings are being saved "permanently".
For example, if for some strange reason, the theme settings are saved inside some Sandboxed area / environment, then the settings are lost when you exit that area.
I don't know why this is happening in your system. Even if for some reason the theme had to be reset when you originally installed Avast, you should be able to save new settings (or save new whole themes), as anyone else can. Maybe something in your theme tools is "corrupted" and you should uninstall it, reboot and reinstall it again.
Have you tried using the common Control Panel options to change a couple of settings, and then reboot? Are those settings also reverted back?