All items disappear after death

Twice since 1.11, my items have vanished upon death (none had the curse of vanishing). It happened after I was killed by mobs (zombie and zombie pigman) and I returned to the death site within 1 minute to find all mobs and all of my items had despawned - including a zombie that picked up my armour. I'm not sure if it affects all deaths, or just zombies.