Steve, your solution worked for me too, and I think I narrowed the problem down further. It’s not whether the PDF pane is on the bottom or on the right that’s the problem, but how many pages it’s displaying. If you keep it on the bottom and zoom out far enough so that you can see 3 pages, the problem comes back. Conversely, if you put it on the right and zoom in so that you just have one page, the problem disappears.
The problem seems to be that the PDF viewer shows whatever page is in the middle of the PDF pane. So if you have several pages showing in the PDF pane and try to scroll slowly in the PDF viewer, you’ll be switched back to whatever is the central page in the PDF pane. If you scroll quickly enough, the PDF pane’s position might change as well, though not necessarily by one page. Whatever page is the center page is what the PDF viewer will end up showing. You can scroll the PDF viewer smoothly without skipping pages by scrolling in the PDF pane instead, though if you’re zoomed out too far you’ll only be able to show pages that reach the middle of the PDF pane, thus rendering the start and end of a PDF unreachable without zooming in the PDF pane. Interestingly, setting the layout to not show the PDF pane doesn’t help, unless you set the zoom level so that only one page is shown before you hide it. However, the zoom level is reset whenever you click a new reference, even if the PDF pane is hidden, so the only way to get this to stick that I can think of at the moment is to show the PDF pane at the bottom where it will automatically choose a zoom level that doesn’t show several pages. Then you can choose whichever view mode you want, including showing the preview pane on the right, as long as you don’t show the PDF pane on the right, which will cause the problem to come back.
Another really weird thing to note is that if you open several different PDFs in the viewer at once and scroll in one of them, the others will change page as well, presumably because they’re all tied to the PDF pane, even though it’s not showing the file. This is of course utterly stupid.
The simplest solution to this bug seems pretty clear to me: don’t tie the page being shown in the PDF viewer to what page is being shown in the PDF pane at all. I can’t think of any reason why I’d want the PDF preview to scroll along as I’m using the PDF viewer in the first place, especially not with the scrolling affecting all open PDFs. I’m going to try to contact customer service and provide them with this information, so that they can hopefully fix the stupid bug. However, the fact that this embarrassing problem hasn’t been fixed for months makes me less than optimistic about a bug fix coming anytime soon.