I have walked around the desert in the new snapshot, and noticed that a few cacti have a missing bottem block or two. When I highlight the missing block with my cursur thing (sorry forgot name of it), it appears to highlight the sand under it. When I destroy the sand, it gets destroyed and the cactus amount of cactus blocks laying on the ground include the invisible one. If the cactus is missing two bottom block and I walk under the visible one, it acts like the cactus is there and hurts me. I generated this world after I had got the snapshot.