When struck by lightning in peaceful mode, villagers and pigs are deleted instantly.
1. /difficulty peaceful
2. /summon villager
3. /summon lightning_bolt
Villager takes damage like any other mob
Villager disappears into thin air
Obviously, this is caused by the villager transforming into a witch (or pig into zombie pigman) and despawning instantly. This transformation is not supposed to occur in peaceful difficulty.