Top of 1 x 2 block bounding box not rendering

When I point my crosshair at the bottom of my two-block-tall block, the whole bounding box is clearly highlighted. However, if I point it at the top, then the bounding box does not render. I know it exists, and is two blocks tall, because I cannot jump over my block. How do I make it render when I hover my crosshair over the top half of the block?