Bug was introduced in October 2009 when Pumpkins (and Red Letters) were added that spawned random monsters.
The data in the field for NPCs (data[29] that should hold the address for where they want to stand/rest accidentlally put into data[29] for the player using the pumpkin data[29] that should have held the kill count of players outside the arena.
This data is now to be reset and lost for anyone who used a pumpkin (or red letter) that spawned an NPC.
119 players had their kill counter reset.
This has now been fixed in the main server.
Well spotted Gambit, although I am really surprised that no one has noticed up until now.