Minecraft Dungeon spawning with only spawner and chest in a geode

 

What I expected to happen was...:
I expected when i found a spawner that it was going to be surrounded with cobblestone and mossy cobblestone but it wasn't.

What actually happened was...:
When I discovered it flying around in spectator i was surprised to see it 

Steps to Reproduce:
1. Create a world with the following seed 5514483333324610036
2. TP to /tp @p 193 -47 994
3. Discover the spawner