After I made a new wold for the snapshot (Like I normally do), I did some stuff on it and then tested with shulkers to see if the bug where they go invisible after you dying to many times still happened. No. it had been fixed. I was then playing around the shulkers, when I stood on one and my game crashed. I restarted and the same thing happened again. The third time, however, it worked, and it didn't crash. A few seconds in, however, and I was kicked because "Flying is not enabled on the server". I was on a single player world, and I wasn't flying, I was on the shulker, so I know that this is a bug.

TL;DR version: Standing on a shulker can get you kicked for flying.