Program: 33831
Project: 33831
Buggy source:
@Override public void run(){
  Island island=plugin.getGrid().getIsland(targetPlayer);
  final IslandPreLevelEvent event=new IslandPreLevelEvent(targetPlayer,island,score);
  event.setLongPointsToNextLevel(pointsToNextLevel);
  plugin.getServer().getPluginManager().callEvent(event);
  long oldLevel=plugin.getPlayers().getIslandLevel(targetPlayer);
  if (!event.isCancelled()) {
    if (oldLevel != event.getLevel()) {
      plugin.getPlayers().setIslandLevel(targetPlayer,event.getLevel());
      plugin.getPlayers().save(targetPlayer);
    }
    if (plugin.getPlayers().inTeam(targetPlayer)) {
      for (      UUID member : plugin.getPlayers().getMembers(targetPlayer)) {
        if (plugin.getPlayers().getIslandLevel(member) != event.getLevel()) {
          plugin.getPlayers().setIslandLevel(member,event.getLevel());
          plugin.getPlayers().save(member);
        }
      }
    }
    if (plugin.getPlayers().inTeam(targetPlayer)) {
      UUID leader=plugin.getPlayers().getTeamLeader(targetPlayer);
      if (leader != null) {
        TopTen.topTenAddEntry(leader,event.getLongLevel());
      }
    }
 else {
      TopTen.topTenAddEntry(targetPlayer,event.getLongLevel());
    }
  }
  final IslandPostLevelEvent event3=new IslandPostLevelEvent(targetPlayer,island,event.getLongLevel(),event.getLongPointsToNextLevel());
  plugin.getServer().getPluginManager().callEvent(event3);
  if (!event3.isCancelled()) {
    if (sender != null) {
      if (!(sender instanceof Player)) {
        if (!report) {
          Util.sendMessage(sender,ChatColor.GREEN + plugin.myLocale().islandislandLevelis.replace("String_Node_Str",String.valueOf(plugin.getPlayers().getIslandLevel(targetPlayer))));
        }
 else {
          for (          String line : reportLines) {
            Util.sendMessage(sender,line);
          }
          Util.sendMessage(sender,ChatColor.GREEN + plugin.myLocale().islandislandLevelis.replace("String_Node_Str",String.valueOf(plugin.getPlayers().getIslandLevel(targetPlayer))));
          if (event.getLongPointsToNextLevel() >= 0) {
            String toNextLevel=ChatColor.GREEN + plugin.myLocale().islandrequiredPointsToNextLevel.replace("String_Node_Str",String.valueOf(event.getLongPointsToNextLevel()));
            toNextLevel=toNextLevel.replace("String_Node_Str",String.valueOf(plugin.getPlayers().getIslandLevel(targetPlayer) + 1));
            Util.sendMessage(sender,toNextLevel);
          }
        }
      }
 else {
        if (!report) {
          if (plugin.getPlayers().getIslandLevel(targetPlayer) != oldLevel) {
            plugin.getMessages().tellOfflineTeam(targetPlayer,ChatColor.GREEN + plugin.myLocale().islandislandLevelis.replace("String_Node_Str",String.valueOf(plugin.getPlayers().getIslandLevel(targetPlayer))));
          }
          if (sender instanceof Player && ((Player)sender).isOnline()) {
            String message=ChatColor.GREEN + plugin.myLocale().islandislandLevelis.replace("String_Node_Str",String.valueOf(plugin.getPlayers().getIslandLevel(targetPlayer)));
            if (Settings.deathpenalty != 0) {
              message+="String_Node_Str" + plugin.myLocale(((Player)sender).getUniqueId()).levelDeaths.replace("String_Node_Str",String.valueOf(deathHandicap));
            }
            Util.sendMessage(sender,message);
            if (event.getLongPointsToNextLevel() >= 0) {
              String toNextLevel=ChatColor.GREEN + plugin.myLocale(((Player)sender).getUniqueId()).islandrequiredPointsToNextLevel.replace("String_Node_Str",String.valueOf(event.getLongPointsToNextLevel()));
              toNextLevel=toNextLevel.replace("String_Node_Str",String.valueOf(plugin.getPlayers().getIslandLevel(targetPlayer) + 1));
              Util.sendMessage(sender,toNextLevel);
            }
          }
        }
 else {
          if (((Player)sender).isOnline()) {
            for (            String line : reportLines) {
              Util.sendMessage(sender,line);
            }
          }
          Util.sendMessage(sender,ChatColor.GREEN + plugin.myLocale().islandislandLevelis + "String_Node_Str"+ ChatColor.WHITE+ plugin.getPlayers().getIslandLevel(targetPlayer));
          if (event.getLongPointsToNextLevel() >= 0) {
            String toNextLevel=ChatColor.GREEN + plugin.myLocale().islandrequiredPointsToNextLevel.replace("String_Node_Str",String.valueOf(event.getLongPointsToNextLevel()));
            toNextLevel=toNextLevel.replace("String_Node_Str",String.valueOf(plugin.getPlayers().getIslandLevel(targetPlayer) + 1));
            Util.sendMessage(sender,toNextLevel);
          }
        }
      }
    }
  }
}

Fixed version (ground truth):
@Override public void run(){
  Island island=plugin.getGrid().getIsland(targetPlayer);
  final IslandPreLevelEvent event=new IslandPreLevelEvent(targetPlayer,island,score);
  event.setLongPointsToNextLevel(pointsToNextLevel);
  plugin.getServer().getPluginManager().callEvent(event);
  long oldLevel=plugin.getPlayers().getIslandLevel(targetPlayer);
  if (!event.isCancelled()) {
    if (oldLevel != event.getLevel()) {
      plugin.getPlayers().setIslandLevel(targetPlayer,event.getLevel());
      plugin.getPlayers().save(targetPlayer);
    }
    if (plugin.getPlayers().inTeam(targetPlayer)) {
      for (      UUID member : plugin.getPlayers().getMembers(targetPlayer)) {
        if (plugin.getPlayers().getIslandLevel(member) != event.getLevel()) {
          plugin.getPlayers().setIslandLevel(member,event.getLevel());
          plugin.getPlayers().save(member);
        }
      }
    }
    if (plugin.getPlayers().inTeam(targetPlayer)) {
      UUID leader=plugin.getPlayers().getTeamLeader(targetPlayer);
      if (leader != null) {
        TopTen.topTenAddEntry(leader,event.getLongLevel());
      }
    }
 else {
      TopTen.topTenAddEntry(targetPlayer,event.getLongLevel());
    }
  }
  final IslandPostLevelEvent event3=new IslandPostLevelEvent(targetPlayer,island,event.getLongLevel(),event.getLongPointsToNextLevel());
  plugin.getServer().getPluginManager().callEvent(event3);
  if (!event3.isCancelled()) {
    if (sender != null) {
      if (!(sender instanceof Player)) {
        if (!report) {
          Util.sendMessage(sender,ChatColor.GREEN + plugin.myLocale().islandislandLevelis.replace("String_Node_Str",String.valueOf(plugin.getPlayers().getIslandLevel(targetPlayer))));
        }
 else {
          for (          String line : reportLines) {
            Util.sendMessage(sender,line);
          }
          Util.sendMessage(sender,ChatColor.GREEN + plugin.myLocale().islandislandLevelis.replace("String_Node_Str",String.valueOf(plugin.getPlayers().getIslandLevel(targetPlayer))));
          if (event.getLongPointsToNextLevel() >= 0) {
            String toNextLevel=ChatColor.GREEN + plugin.myLocale().islandrequiredPointsToNextLevel.replace("String_Node_Str",String.valueOf(event.getLongPointsToNextLevel()));
            toNextLevel=toNextLevel.replace("String_Node_Str",String.valueOf(plugin.getPlayers().getIslandLevel(targetPlayer) + 1));
            Util.sendMessage(sender,toNextLevel);
          }
        }
      }
 else {
        if (!report) {
          if (plugin.getPlayers().getIslandLevel(targetPlayer) != oldLevel) {
            plugin.getMessages().tellOfflineTeam(targetPlayer,ChatColor.GREEN + plugin.myLocale().islandislandLevelis.replace("String_Node_Str",String.valueOf(plugin.getPlayers().getIslandLevel(targetPlayer))));
          }
          if (sender instanceof Player && ((Player)sender).isOnline()) {
            String message=ChatColor.GREEN + plugin.myLocale(((Player)sender).getUniqueId()).islandislandLevelis.replace("String_Node_Str",String.valueOf(plugin.getPlayers().getIslandLevel(targetPlayer)));
            if (Settings.deathpenalty != 0) {
              message+="String_Node_Str" + plugin.myLocale(((Player)sender).getUniqueId()).levelDeaths.replace("String_Node_Str",String.valueOf(deathHandicap));
            }
            Util.sendMessage(sender,message);
            if (event.getLongPointsToNextLevel() >= 0) {
              String toNextLevel=ChatColor.GREEN + plugin.myLocale(((Player)sender).getUniqueId()).islandrequiredPointsToNextLevel.replace("String_Node_Str",String.valueOf(event.getLongPointsToNextLevel()));
              toNextLevel=toNextLevel.replace("String_Node_Str",String.valueOf(plugin.getPlayers().getIslandLevel(targetPlayer) + 1));
              Util.sendMessage(sender,toNextLevel);
            }
          }
        }
 else {
          if (((Player)sender).isOnline()) {
            for (            String line : reportLines) {
              Util.sendMessage(sender,line);
            }
          }
          Util.sendMessage(sender,ChatColor.GREEN + plugin.myLocale().islandislandLevelis + "String_Node_Str"+ ChatColor.WHITE+ plugin.getPlayers().getIslandLevel(targetPlayer));
          if (event.getLongPointsToNextLevel() >= 0) {
            String toNextLevel=ChatColor.GREEN + plugin.myLocale().islandrequiredPointsToNextLevel.replace("String_Node_Str",String.valueOf(event.getLongPointsToNextLevel()));
            toNextLevel=toNextLevel.replace("String_Node_Str",String.valueOf(plugin.getPlayers().getIslandLevel(targetPlayer) + 1));
            Util.sendMessage(sender,toNextLevel);
          }
        }
      }
    }
  }
}