The bug

When a charged creeper explodes and, additionally to a mob which can drop a skull, there are zombie variants (e.g. husk) around, no skull might be dropped.

Reproduction steps

1. Summon a charged creeper

   /summon creeper ~ ~ ~ {powered:1b,NoAI:1b}
   

2. First summon a zombie variant (e.g. a husk)
3. Then summon a mob which can drop a skull (e.g. a wither skeleton) in the same chunk
   Note: The order of summoning the mobs is important (and depends on implementation details) because it determines in which order the explosion kills them.
4. Ignite the creeper by right clicking it with a flint and steel
   No skull is dropped

Code analysis

Mojang names

net.minecraft.world.entity.monster.Zombie.dropCustomDeathLoot(DamageSource, int, boolean) calls increaseDroppedSkulls() before actually making sure that the zombie variant can drop a skull.