[tomsem]

Calibre (by default) groups books by a given author below a single folder, does it not? maybe Kindle reindexes everything in the folder when anything changes in there. That would be a bug, but not one you'd encounter normally.

Note that Kindle Touch has changed the way it organizes content from Amazon (creates a subfolder for each book to contain that book's 'sidecar' files). I would not be surprised if their testing didn't include calibre scenario.