The bug

As of 18w43a, the first 1.14 snapshot, the "hitbox" for the cursor is incorrectly aligned for book click/hover events, meaning you can sometimes click the line above accidentally instead of what your cursor was hovering over.

How to reproduce

/give @p minecraft:written_book{pages:["{\"text\":\"Link to PAGE 2\",\"color\":\"blue\",\"clickEvent\":{\"action\":\"change_page\",\"value\":\"2\"},\"hoverEvent\":{\"action\":\"show_text\",\"value\":{\"text\":\"Hover text\"}}}]","[\"\",{\"text\":\"This is PAGE 2\"}]"],title:"Test Book",author:"?"} 

 Hover your mouse over the top half of the line.

Here is a video demonstration: https://youtu.be/0GVYpVo99Jk