Having written some files to a selection of files I drag another directory to mp3tag to replace the listing. As expected, no files are (apparently) selected, but selecting a track and editing its tags results in the data from the first track being written to the same number of files that were selected in the previous listing.
That does sound similar to the previous bug - I've tried to reproduce what you're seeing, but I don't get the same results.
Could you spell out exactly what you're doing, keystroke by keystroke? In particular, when you're saving, are you pressing the "save" icon, using the menu, clicking on another field of the same file, clicking on another file, etc.?