Originally Posted by HarryT
I'm pretty sure that Amazon's synching mechanism works off the ASIN identifier that's inside the book - and neither removing the DRM nor changing the title alters that. This is illustrated by the fact that Amazon's servers will still show you the "popular highlights" in a book even after you've removed the DRM and changed the title.
Once I finished adding my touches to a book through Calibre. Amazon sees it as two different books. This is why I send it through the Pdoc cloud feature.