Double Tallgrass generated in a new world ( over a lake) crash the game due to having no viable property ( Only if you use f3 on them to see the information about the block). It renders as a double tallgras peony bush. The game deletes those if you unload and reload the chunk. Not knowing exactlly why it didn't delete those the first time, but i did used a swiftness potion II and i was running in the dirrection of the lake ( Coincidence, not knowing it was there. Maybe i didn't left the generator enough time to delete the corrupted blocks?..). This is not the place to post a crash report, but due to the environment ( The crash report doesn't offer all of the informations) i was forced to post it here.