I have an extremely fast clock running this command:
execute @e[type=WitherSkull] ~ ~ ~ particle happyVillager ~ ~1 ~ 0.3 4 0.3 0 5
It runs fine until a few minutes later when the game starts to lag (it is not framerate lag it closely resembles server lag) then upon reloading the world, the game crashes (crash log attached). After the crash the world loads fine.

UPDATE (14w30c) : A few snapshots back they resolved this crash. Although the game no longer crashes after a while of game-play on the world, which is full of running redstone, there is still the same odd lag that was present before. To resolve it you have to exit the game and restart it. I Have no clue what causes it as there are many things running. I will attach the world for further testing!