Comment 3 for bug 1856472

The viewer is *not* a paper book. It is not supposed to behave like one.
In particular using the left and right arrow keys means you can scroll by
just one "page" at a time, instead of by screen-fulls (2 pages in your
case). Therefore there always has to be a blank page at the end of every
chapter, so that it is possible to scroll to have only the last page
visible on screen.

And note that this means that for chapters that have
an odd number of pages, the last page turn behaves just like all
previous page turns, otherwise it would either skip the last page, or
scroll by only a single page, which would give the same sense of
disorientation you experience scrolling backwards.

Since scrolling forwards is more common than scrolling backwards I prefer
to optimize for the former rather than the latter.

That said, I can certainly have the viewer go back to same view when
scrolling backwards soon after scrolling forwards over a chapter
boundary.