unusedfiles.py tags orphan files, however on each run, it tags again the files even if they were tagged previously. Please prevent the bot from tagging the image again if already tagged. Thank you.
I'm afraid I don't know how to explain further. Please see https://meta.wikimedia.org/w/index.php?title=File:Head_logo.jpg&action=history for the issue (just one random file chosen, although they're more).
I've changed the template in my local repo, so it's not the same as in rPWBC, but it should still work.
I think it is insufficient to check for the template only. Looking at the file page I found an additional but still undocumented parameter for the template. I guess the bot script should be changed to tag this new parameter too.