I'm testing this on GNU/Linux but I'm guessing you'll be able to see this behavior on any OS.

Saving changes alters which files are selected (reducing the set to 1). Which file is still selected appears to be random. Also, the file list is scrolled for no apparent reason.

Steps to reproduce:
1. Open EasyTAG on any folder with EasyTAG-modifiable files (the filetype doesn't matter but I used FLAC files). You should pick a folder with more files than EasyTAG can show in the file list view.
2. Select some files (contiguous selection or discontiguous selection, it doesn't matter).
3. Click the save button or press Control-S to save the files. You need not change anything to see the behavior described in the next step.
4. There is only one file selected(!). If your file list was long enough to be scrollable in the EasyTAG file list, that one file is scrolled to the top of the file list(!).

I don't think the selection should have changed at all and if nothing in the sorting of the new files changed the list order, I don't think the list should have been scrolled at all.

It would help to not alter the file selection so one could apply further changes to a (possibly complex) set of files without having to reselect them.