If you try to edit a default template, you'll get:
"You are attempting to edit a default template. Any changes you make to this template may be lost when you next upgrade WebGUI. To be safe, you should make a duplicate of this template.
Duplicate this template and edit."
However, having duplicated and updated the website, you'll get the same message again and a user doesn't know, waht to do.
(Happens in stable and beta)