I was using the /fill command to clean up a savanna biome from fires caused by the new /summon LightningBolt command. I was flying toward a patch of fire and my game crashed. No lag at all, Minecraft just closed and told me you guys couldn't accept my report because my game is modded, although it's not. It did not show the "Is Modded" tag, so I don't know the extent of its belief in my mods.