A couple of suggestions for the Case Conversion changes (in English at least):
- Case should not be changed for letters following a '/' or a ',' (slash or comma)
- Case should not be changed when the next character is a single quote (or apostrophe)
Check the action of the type "case conversion":
There you can define which letters delimit the start of the next word.
If you leave out the characters you mentioned then you should get the desired results.
BTW: How should MP3tag be able to tell it is "English"?
Perhaps you have a look at this thread for proper English case conversion: /t/15863/1