Mine acts a little differently. If I back-page, the first three screen changes will be fast, then slow after that. Happens even if I go forward five pages (screens, whatever), then back again.
Not that big a deal since I don't usually have to back up very often. But sometimes I wish it had the ability to go back or forwards say, five or ten pages, if you held down the page-turn button for a couple of seconds. My old Astak reader would do that. Came in handy some times.