/kill Chicken with doMobLoot = false inconsistency

While using a redstone block timer and a system that sets mobdrops to false, kills a chicken, then sets it to true, i found that it was very inconsistent as to wether or not the chicken would drop things. If i set the gamerule manually, then after the second or third chicken I kill, they stop dropping things. This was happening on a Minecraft Realms Trial server that i obtained over the weekend.