Another quick check to avoid issues with NPCs.

src/main/java/com/gmail/nossr50/util/Misc.java

@@ -13,6 +13,7 @@ import org.bukkit.block.BlockState;
 import org.bukkit.block.Furnace;
 import org.bukkit.entity.Entity;
 import org.bukkit.entity.HumanEntity;
+import org.bukkit.entity.NPC;
 import org.bukkit.entity.Player;
 import org.bukkit.event.inventory.InventoryEvent;
 import org.bukkit.inventory.FurnaceInventory;
@@ -60,7 +61,7 @@ public final class Misc {
     }
 
     public static boolean isNPCEntity(Entity entity) {
-        return (entity == null || entity.hasMetadata("NPC") || (mcMMO.isCombatTagEnabled() && entity instanceof HumanEntity && ((HumanEntity) entity).getName().contains("PvpLogger")));
+        return (entity == null || entity.hasMetadata("NPC") || entity instanceof NPC || (mcMMO.isCombatTagEnabled() && entity instanceof HumanEntity && ((HumanEntity) entity).getName().contains("PvpLogger")));
     }
 
     /**