In Old Worlds, blocks 1-16 from the world edge have several issues.

When swimming in water blocks 1-16 away from the world edge, it is impossible to jump out of the water and walk onto land. When trying to walk onto any "not full" blocks (i.e. stairs and carpet) 1-16 from the edge, jumping is required rather than simply walking to ascend. Also, jumping on blocks 1-16 from the world edge causes cobblestone jumping sound effects regardless of the type of block it really is (grass, dirt, etc.).