Now that someone who knows what they're talking about has answered your question I'll give you my brute force solution.
I like to reformat and clean up books from project Gutenberg and elsewhere and I use Sigil for that (see the Sigil forum here for download instructions). When I get a book that has messed up author names, etc. I drag it out of Calibre to my desktop, delete it from Calibre, and then open it in Sigil and fix its metadata in Sigil's nice metadata editor, and then drag it back to Calibre.
Hopefully I immediately notice that it needs fixing since my procedure destroys the tags and whatnot that I added in Calibre.