I've just discovered something which is probably common knowledge to you guys, but I've read a few articles/discussions about templates and never heard this issue brought up before (and I also think it's slightly confusing) so I'm sharing this just to clarify the rules in case anyone didn't know:
There are two types of templates, which I will call:
1. Normal Templates
When you open a Normal Template, it always opens it as a new “Untitled” file, to protect the original template. So hitting Save brings up the “Save As” dialogue.
2. Editable templates
When you open an Editable Template, you are actually editing the template, and hitting Save will always just save (overwrite).
How do you change a template between the two?
To change a Normal Template to an Editable one, simply save the file as a template file, then it becomes editable.
To change an Editable Template back to a Normal Template, you have to do Save As, and save it as a template file, then close the document without saving it again. Now, it's a proper template file again.
(I think this is right but please correct me if I'm wrong. To be honest, I find it a little confusing, and writing all this down wasn't easy!)
Hope this was of some interest to someone.