So far, no syncing love. I upgraded my version of K4PC and loaded the book on it. I went to a location near the back of the book and set a bookmark for my furthest page read (so I could find it again). I closed the book and forced a sync with K4PC.
I then loaded the same book file on my K3, forced a "sync and check for new items" and opened the book. It did not open to the page I bookmarked as my furthest page read. While the book was open I forced a "sync to the furthest page read" and the message you see in the image below. I tried this a few times with no luck.
Have I missed a step?