The page up/down and the up/down arrow keys apply to the list, regardless of which panel has focus. I'm sure that's by design—so the list is always controllable.
My page up/down keys weren't doing anything at all at the time, but now they're back to this behavior. Don't know what happened.
I see now that if you hit the spacebar once you've reached the bottom of the movie information panel, it will jump back to the top of that panel if you uncheck "Do not jump to the next movie when scrolling movie information with SPACE." But there's a problem with it: If you select a movie where all the information fits on one screen and then select a movie where it doesn't (that is, one that has a scrollbar), the spacebar won't trigger a jumping back to the top of the panel for that movie. To fix this, you have to select another movie where all the information doesn't fit on one screen. Then it will work again--until you happen to click on another all-movie-information-on-one-screen movie. This is with PVD 0.9.9.21 BTW and it happens in every skin I've tried.
Similarly, the search box takes keyboard input, regardless of whether it has focus. That works great for a quick as-you-type search—where is space is only needed. If it is, the search box can be given focus with a mouse-click. So I find the "use spacebar for scrolling" option quite usable.
Yes, I would be satisfied with this approach if the above problem were resolved. Its hard to break the habit of reaching for the page up/down keys, but I can see this could be slightly faster overall.
Alternatively, the mouse wheel (if you have one) can be used for scrolling. It works in whichever pane has focus.
Strangely, the mouse wheel no longer works in either pane for me; it never worked as a 'One screen at a time,' but now it doesn't even work as 'The following number of lines at a time.' Could be that I'm now using Windows 7 64-bit whereas I was using 32-bit before.