[A Lurker]

SCREENSHOT 1:

I imported a Word document, manually edited the metadata, and converted it to a mobi file. Here is the screenshot of the Calibre GUI as it appears. Everything looks fine -- both the "Author(s)" field and the "Author sort" have two names. You'd assume the file metadata is correct.

However, I test this with the following steps:

1.) I find the .mobi file in my Calibre Library. I right-click to copy it. Then I save the copy to my desktop.

2.) Then I add the desktop copy to my Calibre Library as though it's a new book. Note that this is the file as-created by Calibre. No further processing has occurred. I've not exported it to a device or directory. So all the metadata should be there. If any is missing, then Calibre didn't include the metadata when it created the new file...

...which you can see in SCREENSHOT 2 turns out to be the case.

Both authors' names are in the "Author(s)" field, but only the first author's name is in the "Author sort" field.

And if I load this book to a Kindle, only the first author's name will appear.

Perhaps in theory the missing second name from the "Author sort" field shouldn't matter... In terms of the information my Kindle displays, it should be relying on the "Author(s)" field, which has both names... The missing name in the sort field should, in theory, simply mean, at most that second name isn't used for sorting purposes... but I can assure you that my Kindle stopped displaying the second author's name and the same time the second name began disappearing from the "Author sort" field.