Players can no longer unilaterally use items on themselves in their inventory. When they try to use an item, they send a PlayerItemUse packet to the server with the item's details. A serverside script can then check the item and either send the packet back to make the item use go through or drop it.
This should clarify the real meaning of the packet and its associated event.
The event itself has been renamed from OnPlayerKillCount to OnWorldKillCount.
David Cernat
Koncord