The small area on the farm has a building area that extends beyond the ground, for buildings like the barn can be built if they're touching the ground and have a good amount floating. Also happens around the boundaries in general.
https://cdn.discordapp.com/attachments/844397752355913759/926240746221219880/unknown.png
https://cdn.discordapp.com/attachments/844397752355913759/926242089216401438/unknown.png
ver 0.8.11.600