Overview
The swell value of creepers, i.e. how close they are to the explosion, is not written to NBT. This means a creeper will never explode if it is constantly saved and reloaded.
Additionally, this is inconsistent with the maxSwell value (NBT tag Fuse) which is written to NBT.
How to reproduce
- Summon a creeper
- Ignite it using flint and steel
- Just before it explodes close and reopen the world
- Alternatively sending an ignited creeper through a dimension resets its swell value
Outcome
The creeper does not immediately explode but instead starts to swell again
