Falling spawners with a defined entity ID do not display the entity within

A falling block entity representing a spawner with associated block data to define a spawned mob will not display the mob inside while it remains a falling block, and the contents only become visible once the block has touched the ground and stopped being an entity.

Command to reproduce: /summon falling_block ~ ~5 ~-5 {BlockState:{Name:"minecraft:spawner"},TileEntityData:{SpawnData:{entity:{id:"minecraft:ghast"}}}}

Expected results: when the spawner is falling, you would see a ghast inside it.

Actual results: there is nothing inside the spawner for the duration it remains in an entity state.