Originally Posted by kingbee
I seem to have stumbled on a workaround ...
I believe that the way the mobi was created is still key to this working. Using your method avoids having to physically copy the mobi to the Kindle but other than that the mobi still needs to have the proper metadata I would think.
The way I understand what people have been writing is that it looks like Calibre is doing something (perhaps the way it copies covers to the /system/thumbnails directory?) when transferring books to the PW that is messing up the cover situation unless you mark the file for sharing. I would consider it a bug if copying (or using the web browser) the same file manually to the PW works and using Calibre does not. There should be a "please don't hose up my cover art" option when transferring