[Mailman-Developers] edited archive folder-edits lost when message posts

I edited the archive index.html folder for my mailing list. I also edited the date.html and subject.html to have the appearance I wanted. Everything looked good until there was a post.

When a post is made to the list all my data is erased and the archive index.html, date.html, and subject.html went back to default.

Why is this?

How can I change the archive files to look the way I want?