I am seeing an issue that was NOT present in 2.91, which seems to have started in 2.91A build for mp4.
I have mp4 files built using mp4box which contain chapters, and some others without.
In versions 2.91 and prior, these files appeared correctly in mp3tag, which each file appearing as 1 row within the list as expected, and could be properly tagged.
Starting version 2.91A, mp3tag creates 1 entry per CHAPTER for the mp4 file, with each chapter appearing as a different track. The files cannot be properly tagged by mp3tag any longer as a result.
I have created a very small sample file to help with the investigation (attached).
I believe mp3tag (all versions) also have this same issue with mkv files, but I don't have any mkv files.. Just remember seeing that behavior when I was experiment with an mkv file a long time ago.
IMG_0752.zip (66.2 KB)