WotLK Loot bug on Death bringer Saurfang

[devilboyhere]

hi there
so we were on icc25 and i was the raid leader and also loot master. after we killed deathbringer saurfang, a raid member immediately went to the box, leaved group and then loot the box!!! and again it wasn't free loot or even group loot! I was the master looter! so we lost the loot. so what we can do now and what we can do to prevent this?!