Increased mob drop civ perk - does NOT appear to work with automated killing

The increased mob drops perk works with manual killing (Sword), but I tried killing over 40 zombies with a magma block and didn't see it trigger even once (telltale indicator being a zombie dropping 3 flesh, normally impossible without Looting). I assume this may be a bug, but if it's intended the hologram at spawn should be updated to indicate this