Originally Posted by eschwartz
The .sdr is removed specifically when a book is deleted through the Kindle interface and ISN'T in your cloud.
I am sorry, but I honestly believe this is not true. I removed books using the Kindle interface and the .sdr folders are still there. I have been using Kindle PaperWhite, firmware 5.3.1, 5.3.3 and 5.3.4, all with the same result.