Villagers/pigs struck by lightning in peaceful difficulty are deleted

The bug

When struck by lightning in peaceful mode, villagers and pigs are deleted instantly.

How to reproduce

1. /difficulty peaceful
2. /summon villager
3. /summon lightning_bolt

Expected results
Villager takes damage like any other mob

Actual results
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.