Not sure of these classify as bugs but they make mp3tag very clunky and cumbersome.
When writing album and artist tags as one file these fields are not updated on a by chapter basis if they already existed. When they were blank the same info is written by chapter as the main file. Couldn't find a way to refer to the single file fields to update the by chapter fields.
When changing any field in the by chapter view every field that is not unique is blanked on the single file view. This is pretty much always the case for the title field.
For now I have to do all the edits twice, once in chapter view and then again in single file view. Perhaps both the file and the chapters could be shown instead of either one?
When editing in chapter view mp3tag sometimes rewrites the file (as it does for single file) but does this instead of once, for almost every chapter.
With larger files with lots of chapters this creates an enormous overhead. Take a 1Gb audiobook with 50 chapters for example.