Minecraft 1.9, Minecraft 1.9.1 Pre-Release 3, Minecraft 1.9.2, Minecraft 16w15a, Minecraft 16w15b, Minecraft 1.9.3 Pre-Release 2, Minecraft 1.9.3 Pre-Release 3, Minecraft 1.9.4, Minecraft 16w20a, Minecraft 16w21a, Minecraft 16w21b, Minecraft 1.10 Pre-Release 1, Minecraft 1.10 Pre-Release 2, Minecraft 1.10, Minecraft 1.10.1, Minecraft 1.10.2, Minecraft 16w33a, Minecraft 16w39b, Minecraft 16w39c, Minecraft 16w40a
The following is the command in question:
DO NOT USE ON VALUED WORLD
After running this command once, the game will crash.
When you re-enter the world and run the same command, the game will crash again but also delete your world (the level.dat file)
Unfortunately this happened to me on a valuable world and so I lost that world. It was also stupid of me not to make any back-ups, but it was only one of the first nights I was working on it, and I shouldn't have to rely on making back-ups.
I believe the problem is when the LeashKnot naturally despawns, the passengers 'pop-off' and cause issues. In both cases, the timing of the crash after spawning seems to be consistent with the lifetime of the LeashKnot.