File Manager - Changing one HTML file updates multiple HTML files

I have several .html files to test against each other and when I make changes to one of these files in the File manager editor, it seems to dynamically update all the other different documents I want to test (with difference source code) to the exact same source code of the file I was editing. I have noticed this before where I would paste in a script on one document and it would be pasted in on the others which was useful. However, recently just changing or adding new code to one file in the editor, it automatically updates the other documents to be that exact same file code. Its very tiresome. Is there a way to disable this functionality? Thanks