Creepers have a chance to explode immediately

I was playing on my void superflat challenge world and my mob farm was working pretty good until BOOM a creeper fell on my head and exploded instantly absolutely destroying my progress. this isn't a big issue just annoying i did all that and lost everything because of a bug, and its a common thing too

how to replicate (build a old school mob farm where the mobs drop to half a heart then enter the chamber with the loot and wait for a creeper)