Aha! I didn't yet get a chance to run it the way you asked because I was adding some books to the DB and it automatically updated the news.
Because of the setting in the Interface setting of Configuration, Automatically send downloaded news to ebook reader is selected. So whereas the other times, I manually highlighted the entry in the list and clicked the Send to device button, this time they transferred automatically. And guess what? The files it copied to the Kindle when it did it automatically via the Configuration did not include the - calibre in the filename.
Transferred filenames this time, using only the automatic transfer are:
So now I've definitely figured out why the dupe filenames. The above names are what is transferred when you rely on calibre to send the files on it's own via that Config setting. But if I now click the "Send to Kindle" button, I also get the files named:
And THAT is how I'm winding up with duplicates transferred to the Kindle.
I still think this needs to be fixed up. At the very least, if the files are going to be automatically transferred, then the ones transferred manually should have the same name as those transferred automatically so this kind of thing doesn't happen.