This is affected by anyone who plays minecraft. When a player kills a villager, and the villager is doing it's death animation, strike it with lightning and the villager will turn into a burning Witch. Bug or not, this is very strange cause the villager dies, and then a somewhat healthy witch comes to life out of it when struck.
Linked issues
duplicates 1
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Hi Michael, This issue still happens in the recent versions such as 1.10, 1.10.2, and 16w43a. I will update the ticket as explained in your comment, thank you.

Forward-resolved in favor of better explanation in MC-114559
Is this still an issue in the most recent versions (currently that is 1.10.2, or 16w43a) of Minecraft? If so, please update the affected versions and help us keeping this ticket updated from time to time. If you are the owner/reporter of this ticket, you can modify the affected version(s) yourself.