actually, i figured out why on at least one map. On Death star CTF Galactic Civil War, i had 298-303 kills. I then killed the guy with the flag (he was on my team) and lost 257 kills to come out to 41!
Just as the title says, on the PS2 Slim, the Kill counter resets after around 300 kills. The points still say the same, but the kill count says 20 after you've mowed down 320 people. Help?