If you duplicate a rawfile in lighttable and export the original and the duplicate with the following options: target storage = file on disk, “default filename” from select directory, on conflict = create unique filename, file format = copy, then unique filenames are not created. The duplicate overwrites the original.
Works ok if file format = JPEG
There is a detour. You can create unique filenames by specifying the output filename as:
<>\(FILE_NAME)v(VERSION)