[synosure]

This is a really weird thing. If you add dc:rights to your OPF file (as defined in the Dublin Core Metadata Element Set), then convert your epub to mobi, the cover is incorrect in Kindle apps.

To replicate this WITHOUT the bug showing up:
1. Create a well-formed epub that does NOT have dc:rights defined in the metadata.
2. Import the epub into Calibre, then convert it to MOBI.
3. Open the MOBI in Kindle For Mac. The book will display properly and the cover will display properly in the list of books currently installed on your Kindle.

To replicate this WITH the bug showing up:
1. Create a well-formed epub that DOES have dc:rights defined in the OPF metadata. (e.g. <dc:rights>Copyright © John Smith 2010. All rights reserved.</dc:rights>) This bug will really stand out if your epub manuscript has a non-cover image somewhere in it. It also does not matter what letters/characters are in your dc:rights, or how long it is. Its mere existence causes the problem.
2. Import the epub into Calibre, then convert it to MOBI.
3. Open the MOBI in Kindle for Mac. The book will display properly, BUT, in the listing of books currently installed on your Kindle, the cover will be wrong, it will instead show the first image in the manuscript itself.

I did not test this in other (non-Mac) OS versions of Kindle, although I would guess they'd display the same error.

End result, at this time, if you want to use Calibre to convert to mobi for Kindle, do NOT define dc:rights in your OPF file.