FWIW : I changed an author name on a book (test) from 'Nick' to 'con', I got an 267 error and clicked OK, the metadata changed to 'con' but author folder remained as 'Nick' - that may be incongruous but as I understand calibre it's not invalid.
What surprised me was that the book file name remained 'test - Nick.docx' and 'test - Nick.epub'?
Check Library returned no errors.
So how did the OP change the author folder name to CON - in linux maybe?
Added : After I Polished the book I had 'test - Nick.docx' and 'test - con.epub?' and the metadata.opf file had
Code:
<dc:creator opf:file-as="Nick" opf:role="aut">Nick</dc:creator>
<dc:contributor opf:file-as="calibre" opf:role="bkp">calibre (2.53.0)
Interesting
BR