When building at a certain level (16 in this case), blocks become transparent and are missing textures. This happens with any block I place. The attached image shows a block placed at the corresponding level with no texture, making it a "Ghost Block"

The world generated was a Superflat with a setting of one level of air blocks, and nothing else. I summoned in a block and built off of that.

EDIT: Fixed by reloading the world.