Program: 84027
Project: 84027
Buggy source:
public boolean lose(Player player,boolean died){
  Player loser=player;
  Player winner;
  if (starter == player) {
    winner=target;
  }
 else {
    winner=starter;
  }
  loser.sendMessage(Duels.getMessage("String_Node_Str"));
  winner.sendMessage(Duels.getMessage("String_Node_Str"));
  String winnerName=winner.getName();
  String loserName=loser.getName();
  double winnerRating=Duels.highscores.getDouble(winnerName + "String_Node_Str",Duels.STARTING_RATING);
  double loserRating=Duels.highscores.getDouble(loserName + "String_Node_Str",Duels.STARTING_RATING);
  double winnerChance=1 / (1 + Math.pow(10,(loserRating - winnerRating) / 400));
  double outcome;
  if (died && Duels.RANKING_WEIGHT != 0) {
    outcome=((double)winner.getHealth()) / 20;
    outcome=Math.pow(outcome,1 / Duels.RANKING_WEIGHT);
  }
 else {
    outcome=1;
  }
  double change=Duels.RANKING_MAGNITUDE * (outcome - winnerChance);
  Duels.highscores.set(winnerName + "String_Node_Str",winnerRating + change);
  Duels.highscores.set(loserName + "String_Node_Str",loserRating - change);
  Duels.highscores.set(winnerName + "String_Node_Str",Duels.highscores.getInt(winnerName + "String_Node_Str",0) + 1);
  Duels.highscores.set(loserName + "String_Node_Str",Duels.highscores.getInt(loserName + "String_Node_Str",0) + 1);
  Duels.highscores.set(winnerName + "String_Node_Str",Duels.highscores.getInt(winnerName + "String_Node_Str",0) + 1);
  Duels.highscores.set(loserName + "String_Node_Str",Duels.highscores.getInt(loserName + "String_Node_Str",0) + 1);
  if (Duels.economy != null) {
    Duels.economy.depositPlayer(winner.getName(),starterStake + targetStake);
  }
  Duels.duels.remove(winner);
  Duels.duels.remove(loser);
  if (!keepItems) {
    Inventory loserInv=loser.getInventory();
    Inventory winnerInv=winner.getInventory();
    ItemStack[] transfer=loserInv.getContents();
    loserInv.clear();
    for (int i=0; i < transfer.length; i++) {
      if (transfer[i] != null) {
        HashMap<Integer,ItemStack> left=winnerInv.addItem(transfer[i]);
        if (!left.isEmpty()) {
          ItemStack[] drop=(ItemStack[])left.values().toArray();
          winner.getWorld().dropItemNaturally(winner.getLocation(),drop[0]);
        }
      }
    }
    return false;
  }
  return true;
}

Fixed version (ground truth):
public boolean lose(Player player,boolean died){
  Player loser=player;
  Player winner;
  if (starter == player) {
    winner=target;
  }
 else {
    winner=starter;
  }
  loser.sendMessage(Duels.getMessage("String_Node_Str"));
  winner.sendMessage(Duels.getMessage("String_Node_Str"));
  String winnerName=winner.getName();
  String loserName=loser.getName();
  double winnerRating=Duels.highscores.getDouble(winnerName + "String_Node_Str",Duels.STARTING_RATING);
  double loserRating=Duels.highscores.getDouble(loserName + "String_Node_Str",Duels.STARTING_RATING);
  double winnerChance=1 / (1 + Math.pow(10,(loserRating - winnerRating) / 400));
  double outcome;
  if (died && Duels.RANKING_WEIGHT != 0) {
    outcome=(double)winner.getHealth() / 20;
    outcome=Math.pow(outcome,1 / Duels.RANKING_WEIGHT);
  }
 else {
    outcome=1;
  }
  double change=Duels.RANKING_MAGNITUDE * (outcome - winnerChance);
  Duels.highscores.set(winnerName + "String_Node_Str",winnerRating + change);
  Duels.highscores.set(loserName + "String_Node_Str",loserRating - change);
  Duels.highscores.set(winnerName + "String_Node_Str",Duels.highscores.getInt(winnerName + "String_Node_Str",0) + 1);
  Duels.highscores.set(loserName + "String_Node_Str",Duels.highscores.getInt(loserName + "String_Node_Str",0) + 1);
  Duels.highscores.set(winnerName + "String_Node_Str",Duels.highscores.getInt(winnerName + "String_Node_Str",0) + 1);
  Duels.highscores.set(loserName + "String_Node_Str",Duels.highscores.getInt(loserName + "String_Node_Str",0) + 1);
  if (Duels.economy != null) {
    Duels.economy.depositPlayer(winner.getName(),starterStake + targetStake);
  }
  Duels.duels.remove(winner);
  Duels.duels.remove(loser);
  if (!keepItems) {
    Inventory loserInv=loser.getInventory();
    Inventory winnerInv=winner.getInventory();
    ItemStack[] transfer=loserInv.getContents();
    loserInv.clear();
    for (    ItemStack element : transfer) {
      if (element != null) {
        HashMap<Integer,ItemStack> left=winnerInv.addItem(element);
        if (!left.isEmpty()) {
          ItemStack[] drop=(ItemStack[])left.values().toArray();
          winner.getWorld().dropItemNaturally(winner.getLocation(),drop[0]);
        }
      }
    }
    return false;
  }
  return true;
}