Amazon is still changing the author of ebooks I email to my Kindle account from Calibre (and from my email client).
I found a workaround using Amazon's "Send to Kindle" tool. It's an app for Windows that adds a new "Send to Kindle" option into the context menu when you right click on a file.
The app is downloaded directly from Amazon (link below) and setup requires your Kindle (Amazon) account details - Amazon already knows those.
Send to Amazon tool (Windows)
https://www.amazon.com/gp/sendtokindle/pc
I tried it with .mobi files that didn't upload with correct author details previously. I only upload a few books at a time and if my emailed files continue to be altered, it'll do as a workaround for me.
There's a link to the Mac version on the same page, but I haven't tried it.
Hope this helps you too Emma.