I am seeing something very odd since upgrading to v2.85. The TAG column shows 11 files listed instead of the 1 file that is actually in the folder. If I select all of them and run the tagging program, i end up with the one file tagged correctly which is good, but there seems to be a bug here. I have never seen dupes before.
I have attached a couple screen shots... remember there is only one file in the folder that begins with Dirk, and nothing in sub-directories as you can see in the path column.
See the second screen shot. 11 lines, but just 1 file.
To me it looks as though you have discovered the feature that was added with V2.84: nero-style chapters. /t/19270/1
One file with several chapters in it.
the file you're seeing duplicated is most likely a file with MP4 chapters — this means that the file consists of multiple chapters, each of which with accompanying tag information.
You can get rid of the chapter data, by choosing "Strip MP4 chapters" from the right-click context menu.
Let me know if this fixes the issue for you and/or in case you have any open questions.
That context menu did remove the duplicate entries. it takes what seems like an awful lot of time to do it though.
I sure hope you will put an entry into the options section to turn that new functionality off if not needed.