Inventory, chests, furnaces' items disappear when playing a 1.7.4 world in 14w03b

The Structure Spawner v2 (by SethBling) can crash the game in 14w03b and delete the world that the spawner was on. Can cause your WHOLE inventory, even in Survival, to delete itself (if your playing a 14w03b world in 1.7.4 and vice versa).

I do not know how to recover from this. Can someone PLEASE help me?