And I assumed everyone would be reading the first line of the bug report 
With only the latest snapshot (6.14.02) enabled in MultiMC, I launch the game and create a new world. After few seconds the game crashes.
The crash happens in the overworld at spawn, in a fresh world.
I guess the missing block messages only apply to some kind of global block list and not actual blocks in the save file. Otherwise they would not continue appearing as I switch back and forth between the versions repeatedly.