qBittorrent official forums

Ubuntu-19.10, qbittorrent-4.2.1

A few days ago I noticed that my torrent files folder had been altered by having most of the filenames getting ".added" appended to them.
So I assumed this was wrong, and wrote a PHP script to remove ".added", and started to watch more closely.
This morning the same thing happened: "*.mp4.torrent" changed to "*.mp4.torrent.added" for most files.

What is going on?
Is it normal, or wrong ?
Where is it documented ?

Twenty people have read the above post, and no one seems to know the answer, not even "My files have .added too".
There doesn't seem to be ANY documentation.
This would never be allowed in any organisation I have worked in.