I think it would be better if Mp3tag put the special actions (like <keep> and <blank>) at the top of the drop-down boxes when there are several options available.
For example, if there's files with different comments, like "???", "_ROCK_", "... hello?" and so on, they might end up on top of the special actions in the list, making them hard to find.
I'm all for alphabetical sorting of the contents, but these special commands should have a higher priority. This would make it easier to just scroll through the values with the mousewheel instead of having to open the list and read through the entries.