When using negative or higher than 255 Y coordinate, /summon refuses to spawn the entity, while it is otherwise valid for entities to be located at this coordinate.
Comments 7
You can teleport outside of the build limit if you use reletive coordinates ("/tp @p ~0 ~500 ~0" will put you half a km in the air). Also I've messed up commands and voided myself (ok that sounds wrong). The game doesn't want to create anything outside of the build limit but things can travel there after the fact (if you summon a ghast at y250 for example). Watch out. I've done that ghast summon and they turned invulnerable above 255 (damage interactions stopped working between entities). That's probably why the game doesn't want to summon them there.
Is this still a concern in the current Minecraft version 14w18a / Launcher version 1.3.11 or later? If so, please update the affected versions in order to best aid Mojang ensuring bugs are still valid in the latest releases/pre-releases.
Intended; you're not supposed to be out of the world anyway. (You can however use relative coordinates to ./summon or /tp out of the world.)
Negative coordinates are no longer allowed, see MC-45512