Page view "spreads vertically" or "single pages vertically" glitch

When viewing PDFs in Adobe Acrobat, Acrobat defaults to a page view that is analogous to Dorico’s (page view) “Single Pages Vertically”.
For 5+ years I’ve therefore set Sibelius to display in exactly the same way, for the purposes of comparing PDF scores and differing revisions of the same scores in Sibelius.
Now that I’m embracing Dorico I’ve set it to work in the same way in page view.

I think I’ve found a bug, though of course it may be Mac specific:

In “Spreads Horizontally” (the default) and "Single Pages Horizontally) the Home, End, Page Up and Page Down keys on a full size keyboard shunt the pages left, right, up and down. The fn (function) key plus left/right/up/down arrow keys provide the same functionality for those without the extra keys (on a laptop or a standard mac keyboard - Messrs. Jobs & co. decided some years ago that even desktop users shouldn’t need num-keypads).

However, in “Spreads Vertically” and “Single Pages Vertically” these same keys appear to do nothing.

One can still use the scroll bars, two fingers on a trackpad or the clickwheel on a mouse.

The fact that nobody apart from me appears to have reported this in 9+ months means that this presumably isn’t a priority, but if a fix could be added at the very bottom of the to-do list I’d be quite grateful.

Page Up/Page Down do work when you’re viewing pages vertically, but only when the zoom level is such that the width of the single page or spread extends beyond the viewport, i.e. you’re zoomed in enough that you can’t see the edges of the page. This is a bug (and not the only one involving the vertical page arrangement) and will be fixed in future, though I’m not sure when.

Ah yes - so I see! That’s a nice workaround - reducing the width of the window just so it covers the edges of the page.
Many thanks, and as I said, nobody else seems to have mentioned so no rush!