Most paper books have this issue too.
Where the content of the previous page or the next immediate page is visible (depending if you read the left or the right page).
Ghosting is NOT "normal", but it is the standard behaviour for the current level of e-Ink technology. Full page refresh shouldn't really bother you that much. Set it so that it refreshes at each page turn and after a while you'll stop noticing it. The page refreshes in the time it takes for your eyes to go from the bottom of the page to the top, which is still significantly faster than turning an actual page from a book.