Exploding Creepers drop gunpowder when they set off an End Crystal

Place an End Crystal. Spawn/lure a creeper over to the area of the crystal. Make it explode (flint and steel or natural). If it blows up the End Crystal, it will sometimes drop gunpowder. This is not natural because the End Crystal is not killing the Creeper, the creeper is already dead at this point (because it blew up).