I was just wandering what the policy is in regard to this. Myself I have witnessed blatant kill stealing, reported it, but seems that nothing ever happens except i get a reply saying this is being looked into and nothing else.
My understanding is that if one person is in combat with a mob, it is not allowed for another player to come in and steal that mob particularly if it is a higher level player, who can then out damage the mob and take the loot.