In my mind, Ctrl+C, Ctrl+V, Ctrl+X and Ctrl+Z are a standard bunch of shortcuts associated with editing and their behaviour should be the same. Now (in Mp3tag 2.58) we have that Ctrl+C, Ctrl+V and Ctrl+X act differently in Tag panel versus file list, but Ctrl+Z acts the same (which is "undo saving tag").
This could be unimportant, but several times I had a situation when I wanted to undo typing or editing a field in Tag panel, but instead I lost all whe work done in several Tag panel fields! This can be pretty upsetting. The reason is a strong habit that Ctrl+Z is used to undo editing an edit field across all the applications (though, some of them don't have a shortcut for that). I think there are other users with such "mechanical" habit. And I never use "undo saving tag" command, but undoing typing is important for me.
As for now the solution will be disabling Ctrl+Z shortcut: either by means of AutoHotkey or by editing "English.lng". Ok, I've edited "English.lng", it's easier.
Thank you for considering this thing!