Sumatra does not show long page full-screen properly.

[slubslub]

I have two PDFs. The first one:

Number of Pages: 18 Page Size: 19.55 x 11.0 in

The second one is the same as the first, except it is one continuous page:

Number of Pages: 1 Page Size: 19.55 x 198.0 in

The first one of these in full screen shows the page taking up the entire width. This is perfect, you can flip pages with next screen and it is rock-solid the next page.

The second one has thin black margins on each side. The page is shown "full screen" but is not. You can see a bit of the next page at the bottom. Flipping pages means it gets a little bit of the next page each time so you don't have the perfect page-flipping experience of the 18 page PDF.

Why is it doing this?