Program: 34041
Project: 34041
Buggy source:
@EventHandler(priority=EventPriority.LOWEST) public void onInventoryClick(InventoryClickEvent event){
  Player player=(Player)event.getWhoClicked();
  ItemStack clicked=event.getCurrentItem();
  Inventory inventory=event.getInventory();
  int slot=event.getRawSlot();
  if (inventory.getName().equalsIgnoreCase(plugin.myLocale().igsTitle)) {
    if (event.getSlotType() == SlotType.OUTSIDE) {
      player.closeInventory();
      return;
    }
    event.setCancelled(true);
    return;
  }
  if (inventory.getName().equals(plugin.myLocale(player.getUniqueId()).challengesguiTitle)) {
    event.setCancelled(true);
    if (event.getSlotType() == SlotType.OUTSIDE) {
      player.closeInventory();
      return;
    }
    List<CPItem> challenges=plugin.getChallenges().getCP(player);
    if (challenges == null) {
      plugin.getLogger().warning("String_Node_Str");
      player.closeInventory();
      player.performCommand(Settings.CHALLENGECOMMAND);
      return;
    }
    if (slot >= 0 && slot < challenges.size()) {
      CPItem item=challenges.get(slot);
      if (clicked.equals(item.getItem())) {
        if (item.getNextSection() != null) {
          player.closeInventory();
          player.openInventory(plugin.getChallenges().challengePanel(player,item.getNextSection()));
        }
 else         if (item.getCommand() != null) {
          player.performCommand(item.getCommand());
          player.closeInventory();
          player.openInventory(plugin.getChallenges().challengePanel(player));
        }
      }
    }
  }
  if (miniShop != null && inventory.getName().equals(miniShop.getName())) {
    String message="String_Node_Str";
    event.setCancelled(true);
    if (!Settings.useEconomy || slot == -999) {
      player.closeInventory();
      return;
    }
    if (store.containsKey(slot)) {
      MiniShopItem item=store.get(slot);
      if (clicked.equals(item.getItem())) {
        if (event.getClick().equals(ClickType.LEFT)) {
          if (item.getPrice() > 0D) {
            if (!VaultHelper.econ.has(player,Settings.worldName,item.getPrice())) {
              message=(plugin.myLocale().minishopYouCannotAfford).replace("String_Node_Str",item.getDescription());
            }
 else {
              EconomyResponse r=VaultHelper.econ.withdrawPlayer(player,Settings.worldName,item.getPrice());
              if (r.transactionSuccess()) {
                message=plugin.myLocale().minishopYouBought.replace("String_Node_Str",Integer.toString(item.getQuantity()));
                message=message.replace("String_Node_Str",item.getDescription());
                message=message.replace("String_Node_Str",VaultHelper.econ.format(item.getPrice()));
                player.getInventory().addItem(item.getItemClean());
              }
 else {
                message=(plugin.myLocale().minishopBuyProblem).replace("String_Node_Str",item.getDescription());
              }
            }
          }
        }
 else         if (event.getClick().equals(ClickType.RIGHT) && allowSelling && item.getSellPrice() > 0D) {
          if (player.getInventory().containsAtLeast(item.getItemClean(),item.getQuantity())) {
            player.getInventory().removeItem(item.getItemClean());
            VaultHelper.econ.depositPlayer(player,Settings.worldName,item.getSellPrice());
            message=plugin.myLocale().minishopYouSold.replace("String_Node_Str",Integer.toString(item.getQuantity()));
            message=message.replace("String_Node_Str",item.getDescription());
            message=message.replace("String_Node_Str",VaultHelper.econ.format(item.getSellPrice()));
          }
 else {
            message=(plugin.myLocale().minishopSellProblem).replace("String_Node_Str",item.getDescription());
            ;
          }
        }
        if (!message.isEmpty()) {
          player.sendMessage(message);
        }
      }
    }
  }
  for (  String panelName : controlPanel.keySet()) {
    if (inventory.getName().equals(panelName)) {
      if (slot == -999) {
        player.closeInventory();
        event.setCancelled(true);
        return;
      }
      HashMap<Integer,CPItem> thisPanel=panels.get(panelName);
      if (slot >= 0 && slot < thisPanel.size()) {
        String command=thisPanel.get(slot).getCommand();
        String nextSection=ChatColor.translateAlternateColorCodes('&',thisPanel.get(slot).getNextSection());
        if (!command.isEmpty()) {
          player.closeInventory();
          event.setCancelled(true);
          player.performCommand(command);
          return;
        }
        if (!nextSection.isEmpty()) {
          player.closeInventory();
          Inventory next=controlPanel.get(nextSection);
          if (next == null) {
          }
          player.openInventory(next);
          event.setCancelled(true);
          return;
        }
        player.closeInventory();
        event.setCancelled(true);
        return;
      }
    }
  }
}

Fixed version (ground truth):
@EventHandler(priority=EventPriority.LOWEST,ignoreCancelled=false) public void onInventoryClick(InventoryClickEvent event){
  Player player=(Player)event.getWhoClicked();
  ItemStack clicked=event.getCurrentItem();
  Inventory inventory=event.getInventory();
  int slot=event.getRawSlot();
  if (inventory.getName().equalsIgnoreCase(plugin.myLocale().igsTitle)) {
    if (event.getSlotType() == SlotType.OUTSIDE) {
      player.closeInventory();
      return;
    }
    event.setCancelled(true);
    return;
  }
  if (inventory.getName().equals(plugin.myLocale(player.getUniqueId()).challengesguiTitle)) {
    event.setCancelled(true);
    if (event.getSlotType() == SlotType.OUTSIDE) {
      player.closeInventory();
      return;
    }
    List<CPItem> challenges=plugin.getChallenges().getCP(player);
    if (challenges == null) {
      plugin.getLogger().warning("String_Node_Str");
      player.closeInventory();
      player.performCommand(Settings.CHALLENGECOMMAND);
      return;
    }
    if (slot >= 0 && slot < challenges.size()) {
      CPItem item=challenges.get(slot);
      if (clicked.equals(item.getItem())) {
        if (item.getNextSection() != null) {
          player.closeInventory();
          player.openInventory(plugin.getChallenges().challengePanel(player,item.getNextSection()));
        }
 else         if (item.getCommand() != null) {
          player.performCommand(item.getCommand());
          player.closeInventory();
          player.openInventory(plugin.getChallenges().challengePanel(player));
        }
      }
    }
  }
  if (miniShop != null && inventory.getName().equals(miniShop.getName())) {
    String message="String_Node_Str";
    event.setCancelled(true);
    if (!Settings.useEconomy || slot == -999) {
      player.closeInventory();
      return;
    }
    if (store.containsKey(slot)) {
      MiniShopItem item=store.get(slot);
      if (clicked.equals(item.getItem())) {
        if (event.getClick().equals(ClickType.LEFT)) {
          if (item.getPrice() > 0D) {
            if (!VaultHelper.econ.has(player,Settings.worldName,item.getPrice())) {
              message=(plugin.myLocale().minishopYouCannotAfford).replace("String_Node_Str",item.getDescription());
            }
 else {
              EconomyResponse r=VaultHelper.econ.withdrawPlayer(player,Settings.worldName,item.getPrice());
              if (r.transactionSuccess()) {
                message=plugin.myLocale().minishopYouBought.replace("String_Node_Str",Integer.toString(item.getQuantity()));
                message=message.replace("String_Node_Str",item.getDescription());
                message=message.replace("String_Node_Str",VaultHelper.econ.format(item.getPrice()));
                player.getInventory().addItem(item.getItemClean());
              }
 else {
                message=(plugin.myLocale().minishopBuyProblem).replace("String_Node_Str",item.getDescription());
              }
            }
          }
        }
 else         if (event.getClick().equals(ClickType.RIGHT) && allowSelling && item.getSellPrice() > 0D) {
          if (player.getInventory().containsAtLeast(item.getItemClean(),item.getQuantity())) {
            player.getInventory().removeItem(item.getItemClean());
            VaultHelper.econ.depositPlayer(player,Settings.worldName,item.getSellPrice());
            message=plugin.myLocale().minishopYouSold.replace("String_Node_Str",Integer.toString(item.getQuantity()));
            message=message.replace("String_Node_Str",item.getDescription());
            message=message.replace("String_Node_Str",VaultHelper.econ.format(item.getSellPrice()));
          }
 else {
            message=(plugin.myLocale().minishopSellProblem).replace("String_Node_Str",item.getDescription());
            ;
          }
        }
        if (!message.isEmpty()) {
          player.sendMessage(message);
        }
      }
    }
  }
  for (  String panelName : controlPanel.keySet()) {
    if (inventory.getName().equals(panelName)) {
      if (slot == -999) {
        player.closeInventory();
        event.setCancelled(true);
        return;
      }
      HashMap<Integer,CPItem> thisPanel=panels.get(panelName);
      if (slot >= 0 && slot < thisPanel.size()) {
        String command=thisPanel.get(slot).getCommand();
        String nextSection=ChatColor.translateAlternateColorCodes('&',thisPanel.get(slot).getNextSection());
        if (!command.isEmpty()) {
          player.closeInventory();
          event.setCancelled(true);
          player.performCommand(command);
          return;
        }
        if (!nextSection.isEmpty()) {
          player.closeInventory();
          Inventory next=controlPanel.get(nextSection);
          if (next == null) {
          }
          player.openInventory(next);
          event.setCancelled(true);
          return;
        }
        player.closeInventory();
        event.setCancelled(true);
        return;
      }
    }
  }
}