One buggy feature is that Korean Hwacha keeps 200% city attack bonus when is upgraded from Catapult. Since they are designed to deal with the units (not cities), they have twice much higher power then its replacement and don't have city 200% promotion originally. A Hwacha with 200% city attack bonus is truly overpowered.
Due to this, Korea has a unit that is stronger than Great War Infantry (against cities) before the Renaissance era.
Korea is no longer a defensive civ. LoL