Superscript characters in album names (possibly in other fields too, I can't test that) are normalized to baseline versions in both tags and filenames.

Here's a few affected releases:
Physics² normalized to Physics2
Physics¹ normalized to Physics1
Melancholie² normalized to Melancholie2

Attached a screenshot to show what I mean.

While it is possible that path/filenames are normalized for compatibility reasons (however not an issue on POSIX systems), it definitely shouldn't be done in the ID3/OGG/whatever tag.

More info on superscript and subscript