So I spawned a spawner minecart with a command block. The command was the following:

/summon spawner_minecart ~ ~6 ~.1 {SpawnRange:0,MinSpawnDelay:3,MaxSpawnDelay:3,SpawnData:{id:"minecraft:falling_block",Block:redstone_block,Time:1,DropItem:0},SpawnCount:1}

This creates a spawner minecart with a SpawnRange of 0 that spawns redstone blocks, so I expected it to spawn redstone block in the block the spawner minecart is in.

However, the spawner minecart spawns the blocks in the block it is in as well as the block above that, and also the block underneath the block the spawner minecart is standing on.

From 14w06a on, some of the spawned blocks are invisible. They become visible again after relogging.

The weird thing though is, that the spawner minecart doesn't drop blocks below the floor when it is at an exact coordinate. (In the command it said: ~ ~6 ~.1 If you replace the .1 with a 1 it doesn't spawn blocks below the floor, but it still does spawn above the block the spawner minecart is in.)

How to reproduce

1. Use the following command

   /setblock ~ ~4 ~ spawner{SpawnRange:0s,MinSpawnDelay:3s,MaxSpawnDelay:3s,SpawnData:{entity: {id: "minecraft:armor_stand", NoGravity:1b}},SpawnCount:1s} destroy
   

   → All armor stands are spawned at the same x and y position because SpawnRange is 0, but their y position varies

Code analysis

Code analysis by marcono1234 can be found in this comment.