Cave Spiders drop armor

So i was on my survival island world and found myself a cave spider spawner and made a xp/string/spider eye...thing...(i forgot the wording but thats not important).

and when i was playing on hard so i can get more spiders to spawn and such, some started to drop armor when killed. i mean its not supposed to do that, but i dont mind...free armor...but its not supposed to but like that and needs fixing.