Spawnpoint Command Improperly Functions

Setting the spawnpoint to a coordinate where there are no blocks (i.e. in the air, or at a high altitude) will cause the player to spawn at the closest y to the ground. For example, If the y coordinate of the highest block at 0,0 was y67, and I were to set my spawnpoint to 0,250,0, then I would respawn at 0,68,0.