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. Whatever page is the center page is what the PDF viewer will end up showing. If you scroll quickly enough, the PDF pane's position might change as well, though not necessarily by one page. 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.
The problem seems to be that the PDF viewer shows whatever page is in the middle of the PDF pane. Conversely, if you put it on the right and zoom in so that you just have one page, the problem disappears. If you keep it on the bottom and zoom out far enough so that you can see 3 pages, the problem comes back. 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.
Steve, your solution worked for me too, and I think I narrowed the problem down further.
