Newly-generated Mansions replaced by dirt

I was playing on the newest snapshot when I decided to locate a Woodland Mansion with the /locate command. I found one, teleported directly there, and once it finished loading I found that it was halfway inside a small hill. Inside, there were large clumps of dirt hanging from the ceiling. Weirder than that, new dirt blocks were appearing ever couple seconds, and replacing the normal blocks. Further inside, there were more dirt blocks instead of planks, even though that section should not have been in the hill. The same Mansion was also on fire for some reason and had a few farmland blocks sticking out of the side for no discernible reason.