When scrolling down a long topic list with j the red caret will stay on the last topic, with the list scrolling one topic per keypress. When scrolling up again with k, the caret stays on the bottom row and the entire page scrolls up one topic per keypress. This is unnecessarily jarring when there’s a bunch of topics in the list above that the caret could move into without scrolling the page at all.
Compare with Gmail, where scrolling past the last mail thread will scroll the screen down one half page and place the caret in the center of the screen, with plenty of space to move again. Scrolling up uses the same mechanics.
Note that using that scrolling behavior in the downward direction would also give the browser time to load more items, while currently there is a pause when new items need to be loaded. (There’s also a bug I just noticed that the caret will sometimes jump up a screenfull of items than I had already scolled past, when new items need to be fetched.)