Problem writing "Western European" UTF-8 encoded XML file

I am working on a project that uses XMP to write values to an XML file that is "Western European" UTF-8 encoded. Everything works fine for all files of this type unless they contain an exponent/superscript special character like the one at the end of this string ->  “m/s²”.

In any file that I attempt to write one of those characters they are encoded with a value of "-78", while it should be "194 178" according to the UTF-8 spec:

Unicode/UTF-8-character table

This appears to simply be a bug in XMP. I can provide a reproducer if needed. Let me know.

Erik