If you reload the app that was installed on the core ink when you got it and use the thumb wheel on the side to move between the two screens you'll see that it paints the entire screen black between displaying each screen. This is the same solution used on e-ink ebook readers (Kindle, Kobo, etc.) as a solution for ghosting from the previous page; it's an option you can turn on or off in the e-reader's settings. The support people ought to know something as simple as this.