Hardened and stained clay is disappearing and leaving holes in my world

Hardened and stained clay is disappearing and leaving holes in my world

I expected it to stay there.

I came back to some rooms and either the floor, ceiling or doorways were missing

Steps to Reproduce:
1. Place some hardened or stained clay.
2. Wait for a while.
3. Come back and it will have vanished leaving holes in its place.
3. ...