unlike mobs, other entities don't seem to have any limitation to where they can spawn using a modified monster spawner. so if i have a spawner underground that spawns swords, the swords will appear inside the blocks near the spawner.
this is a problem because this means that these spawners can't be shut down, like regular mob spawners.
this is more of a suggestion, but i think non-mob entities should have a 1x1 block spawning requirement, so that these spawners can be turned off using a piston.