[MC-130509] Custom spawners resets to default (pig) state after spawning entity once

Monster spawners with custom data that were created using /give revert to pig spawners after one spawn. For example, activating the command

Minecraft 1.12.2

/give @p minecraft:mob_spawner 1 0 {BlockEntityTag:{SpawnCount:15,SpawnRange:3,MinSpawnDelay:1,MaxSpawnDelay:40,RequiredPlayerRange:1,SpawnData:{id:"minecraft:chest_minecart"}}}

Minecraft 18w22c

/give @p minecraft:mob_spawner{BlockEntityTag:{SpawnCount:15,SpawnRange:3,MinSpawnDelay:1,MaxSpawnDelay:40,RequiredPlayerRange:1,SpawnData:{id:"minecraft:chest_minecart"}}}

WILL give me a monster spawner that spawns a chest minecart, but when that is placed and it spawns one round of entities, the spawner will revert to a pig spawner.