This doesn't really count as a bug, but it's a design decision that really bugs (horrible pun, I know) me.
When doing extended reading I like to use 1 column mode so I can turn pages with my directional keys. When in this mode, there are two arrows pointing horizontally in the bottom right of the pane. That makes sense when applied to the convention of turning pages in a book; however, the left and right arrows do not turn the pages! While the arrow points left/right, the up/down keys change pages.
It should be consistent in both places (or just enable left/right and up/down keys to change pages). Not a big thing, but I do consistently hit the left/right arrows because of it.