I'm not sure if this has been covered yet (pardon me if it has).
Editing "large" fields in the Action Window isn't always as user friendly as in MC11. For example, when editing a tag like Lyrics, Bios, or Review the Action Window conveniently changes to give the user a larger workspace to type or edit. However, when I'm done making changes there is no on-screen indication of what I do next. There is no "Save" button. The only available options are to click "Action Window" which returns the user to the last screen without saving or to click the "X" which actually does save the changes and returns to the top of the tags list.
Windows users are trained to recognize the "X" as a close button so it's counter intuitive to use the "X" as a "Save and return" function. I just think adding a real "Save" button would be helpful in terms of UI.
Also, after saving the edited field the user is returned to the top of the Tag screen. IMO, returning to the top of the list is not the way to do it. I want to see my saved data so I think returning to the Tag screen at the point the last tag save was made would be better. If I edit the Lyrics field and save it should return me to the Tag screen but automatically scrolled down to the Lyrics field (in the alphabetical list). That way I can confirm the tag was, in fact, saved.