Minecraft wiki entry for Historical_effects, associated text: After 1,048,576 blocks, the first breakdown of hitboxes can be witnessed for cakes and cacti. Previously, their hitboxes would perfectly fit their cuboidal shape, however any placed past this point would experience a minor distortion; the hitboxes would be stretched to a full block width on whatever axis this distance was surpassed on. This also affects their collision boxes - previously pressing against these on their negative-facing side would get a value of .76250, but after this point this value is now .70000, like a full block. Cacti can still cause damage with this expanded hitbox.