The bug

Mob heads will only drop the first time the /damage command is used, even though the charged creeper entity is still in the world after the /damage command is used.

Video:
https://www.youtube.com/watch?v=LAG-VTj59yQ

Reproduce steps

1. Summon a charged creeper.

   /summon minecraft:creeper ~ ~ ~ {powered:1b}

2. Summon a wither skeleton.

   /summon minecraft:wither_skeleton ~ ~ ~

3. Use the /damage command:

   /damage @e[type=minecraft:wither_skeleton,limit=1] 30 minecraft:explosion by @e[type=minecraft:creeper,limit=1] from @e[type=minecraft:creeper,limit=1]

4. It is found that the first use of the /damage command will drop the mob head.
5. Summon a wither skeleton again.
6. Use the /damage command again.
7. Found that the mobs no longer drop their heads, even though the target charged creeper entity still exists in the world.