1. Open a print preview window.  It starts out in "Zoom to fit whole page" mode,
but you can click this (second magnifying glass) again to make sure.
2. Press page-down.  It scrolls, a teeny bit.  (There's 3 pixels of scroll
possible in fit-to-page zoom mode.)

Expected: If the page is really fit to the window, no scrolling should be possible.

The upshot of this is that if you press "page down" to go to the next page, you
have to press it twice for every page: the first time you press it, it scrolls 3
pixels down to the bottom of the page, which is easily missed if you aren't
watching carefully.

If I start on page 1 in fit-to-window mode and press page-down 4 times, for
example, I end up on page 3, but I think I should be on page 5.

This makes it especially confusing to explain to people.  ("Page-down to page 3
... er, you have to hit page-down a couple more times now ... um, that's
because...")