That's because there is nothing down there, the set of items fits the window perfectly. The reason you see more books in the search is because some are coming from the tools section.
I've been seeing this since the beginning of Minecraft. The problem is that the game only plays the block noise for the nearest block under you to avoid overlapping noises. If more than 50% of you is off the edge of the block the block chosen for noise in an air block. This also effects the player's movement for certain blocks such as ice, which will cause the player to slide even if they are not completely on them.
I've seen this many times, of course there has to be some order in which the chunks are chosen to be rendered, but It sorta seems like the priorities aren't properly chosen.
Your screenshots seem to be working against you here, they appear to be showing a Gordan Freeman skin.