Mobs on a team dont increment killedbyteam score from any player they kill

okay, so i have to track how many kills a team has, thats all fine, but i have a class that can spawn mobs on his team, but strangly, mobs on a team dont increment the KilledbyTeam score of any player they kill!

i have added some screen shots to show what i mean

what i did was:
1: create a zombie that is on team blue
2: create a objective that tracks killedbyteam.blue, and show it on the side bar
3 :get killed by said zombie
4: score doesnt increase, even through the zombie is on team blue

what i expected, would be that, because your technically killed by the blue team, it would increase the score, but no :x