What is even more interesting (to me at least) is this:
1. I buy a book on Amazon and choose my K4PC program in the "Deliver To" box.
K4PC is not running on my PC.
2. I start up K4PC on my PC - and sync it - but no new books appear.
3. BUT - the new books do download into the My Kindle Content folder on my PC - but don't show up in the K4PC program.
4. Closing and then restarting K4PC then results is the books appearing in the K4PC program.
So - when you open K4PC and sync it - the books actually download onto your PC, but it takes a restart of K4PC to find them.