Well, I don't know if it's a bug or lag, I guess it's a bug..
It happends sometime that you'r killing someone, but it still doesn't show you "you've killed bla" and not writing in the consol as well, but it's adding to your killing count..
It's kinda annoying bug coz you'r trying to keep shoting him since he seems to be alive some of the times..
(that's happends to me once a while while i'm playing with 100 ping)
Sorry if it was reported already but just wanted you to know.