A couple of players (names I can't remember :/) that I've played against have been using some sort of multiple med-pack cheat. Basically, every time I hit them they were popping a medpack.
This isn't just a lag problem and it wasn't multiple humans hitting meds near each other. The first time I ran across this was on Niveus about two weeks ago, I was a dretch and I was chasing a human through the tunnel system on the ground floor, both of us were on our own. After every bite (unfortunately I couldn't quite get the headshot) he'd take another medpack, essentially voiding any damage I did to him.
It just happened again, this time in the Beer Garden server on the Tremor map. Same deal, only this time he was sort of camping in front of the human main entrance with a lasgun.
I'm not sure what can be done about this, next time I see it happen I'll try to spec and record anyway.