[MC-10461] Falling spawner does not work when stacked in an entity

Falling spawner does not work when stacked in an entity, it flickers between its current position and its original position(before i was stacked), and then dissapears.

When trying to spawn those entities in 15w31a, "data tag parsing failed unbalanced brackets" error appears.

/summon FallingSand ~ ~1 ~ {Block:0,Time:1,DropItem:0,Riding:{id:"FallingSand",Block:0,Time:1,DropItem:0}}
/summon FallingSand ~ ~1 ~ {Block:0,Time:1,DropItem:0,Riding:{id:"Cow",Riding:{id:"FallingSand",Block:0,Time:1,DropItem:0}}}
/summon Pig ~ ~1 ~ {Riding:{id:"Pig",Riding:{id:"FallingSand",Block:mob_spawner,Time:1,DropItem:0,Riding:{id:"Bat"}}}}