Program: 51689
Project: 51689
Buggy source:
@Override public void simpleMode(InventoryClickEvent event){
  Player p=(Player)event.getWhoClicked();
  DecimalFormat f=new DecimalFormat("String_Node_Str");
  boolean top=event.getView().convertSlot(event.getRawSlot()) == event.getRawSlot();
  if (top) {
    if (event.getSlot() >= getInventory().getSize() - 1) {
      if (isWool(event.getCurrentItem(),(byte)14)) {
        switchInventory(TraderStatus.PLAYER_SELL);
      }
 else       if (isWool(event.getCurrentItem(),(byte)3)) {
        switchInventory(TraderStatus.PLAYER_SELL);
      }
 else       if (isWool(event.getCurrentItem(),(byte)5)) {
        switchInventory(TraderStatus.PLAYER_BUY);
      }
    }
 else     if (equalsTraderStatus(TraderStatus.PLAYER_SELL)) {
      if (selectItem(event.getSlot(),TraderStatus.PLAYER_SELL).hasSelectedItem()) {
        if (getSelectedItem().hasMultipleAmouts()) {
          switchInventory(getSelectedItem());
          setTraderStatus(TraderStatus.PLAYER_SELL_AMOUNT);
        }
 else {
          if (getClickedSlot() == event.getSlot()) {
            if (buyTransaction(p,getSelectedItem().getPrice()))             p.sendMessage(ChatColor.GOLD + "String_Node_Str" + getSelectedItem().getAmount()+ "String_Node_Str"+ f.format(getSelectedItem().getPrice())+ "String_Node_Str");
 else             p.sendMessage(ChatColor.GOLD + "String_Node_Str");
          }
 else {
            p.sendMessage(ChatColor.GOLD + "String_Node_Str" + f.format(getSelectedItem().getPrice())+ "String_Node_Str");
            p.sendMessage(ChatColor.GOLD + "String_Node_Str");
            setClickedSlot(event.getSlot());
          }
        }
      }
    }
 else     if (equalsTraderStatus(TraderStatus.PLAYER_SELL_AMOUNT)) {
      if (!event.getCurrentItem().getType().equals(Material.AIR)) {
        if (getClickedSlot() == event.getSlot()) {
          if (buyTransaction(p,getSelectedItem().getPrice(event.getSlot())))           p.sendMessage(ChatColor.GOLD + "String_Node_Str" + getSelectedItem().getAmount(event.getSlot())+ "String_Node_Str"+ f.format(getSelectedItem().getPrice(event.getSlot()))+ "String_Node_Str");
 else           p.sendMessage(ChatColor.GOLD + "String_Node_Str");
        }
 else {
          p.sendMessage(ChatColor.GOLD + "String_Node_Str" + f.format(getSelectedItem().getPrice(event.getSlot()))+ "String_Node_Str");
          p.sendMessage(ChatColor.GOLD + "String_Node_Str");
        }
      }
    }
    setInventoryClicked(true);
  }
 else {
    if (equalsTraderStatus(TraderStatus.PLAYER_BUY)) {
      if (selectItem(event.getSlot(),TraderStatus.PLAYER_BUY).hasSelectedItem()) {
        if (getClickedSlot() == event.getSlot()) {
          if (sellTransaction(p,getSelectedItem().getPrice(event.getSlot())))           p.sendMessage(ChatColor.GOLD + "String_Node_Str" + event.getCurrentItem().getAmount()+ "String_Node_Str"+ f.format(getSelectedItem().getPrice() * event.getCurrentItem().getAmount())+ "String_Node_Str");
        }
 else {
          p.sendMessage(ChatColor.GOLD + "String_Node_Str" + f.format(getSelectedItem().getPrice() * event.getCurrentItem().getAmount())+ "String_Node_Str");
          p.sendMessage(ChatColor.GOLD + "String_Node_Str");
          setClickedSlot(event.getSlot());
        }
      }
    }
 else     if (selectItem(event.getSlot(),TraderStatus.PLAYER_BUY).hasSelectedItem()) {
      if (getClickedSlot() == event.getSlot() && !getInventoryClicked()) {
        if (sellTransaction(p,getSelectedItem().getPrice(event.getSlot())))         p.sendMessage(ChatColor.GOLD + "String_Node_Str" + event.getCurrentItem().getAmount()+ "String_Node_Str"+ f.format(getSelectedItem().getPrice() * event.getCurrentItem().getAmount())+ "String_Node_Str");
      }
 else {
        if (!event.getCurrentItem().equals(new ItemStack(Material.WOOL,1,(short)0,(byte)3)) && !event.getCurrentItem().getType().equals(Material.AIR)) {
          p.sendMessage(ChatColor.GOLD + "String_Node_Str" + f.format(getSelectedItem().getPrice() * event.getCurrentItem().getAmount())+ "String_Node_Str");
          p.sendMessage(ChatColor.GOLD + "String_Node_Str");
          setClickedSlot(event.getSlot());
        }
      }
    }
    setInventoryClicked(false);
  }
  event.setCancelled(true);
}

Fixed version (ground truth):
@Override public void simpleMode(InventoryClickEvent event){
  Player p=(Player)event.getWhoClicked();
  DecimalFormat f=new DecimalFormat("String_Node_Str");
  boolean top=event.getView().convertSlot(event.getRawSlot()) == event.getRawSlot();
  if (top) {
    if (event.getSlot() >= getInventory().getSize() - 1) {
      if (isWool(event.getCurrentItem(),(byte)14)) {
        switchInventory(TraderStatus.PLAYER_SELL);
      }
 else       if (isWool(event.getCurrentItem(),(byte)3)) {
        switchInventory(TraderStatus.PLAYER_SELL);
      }
 else       if (isWool(event.getCurrentItem(),(byte)5)) {
        switchInventory(TraderStatus.PLAYER_BUY);
      }
    }
 else     if (equalsTraderStatus(TraderStatus.PLAYER_SELL)) {
      if (selectItem(event.getSlot(),TraderStatus.PLAYER_SELL).hasSelectedItem()) {
        if (getSelectedItem().hasMultipleAmouts()) {
          switchInventory(getSelectedItem());
          setTraderStatus(TraderStatus.PLAYER_SELL_AMOUNT);
        }
 else {
          if (getClickedSlot() == event.getSlot()) {
            if (buyTransaction(p,getSelectedItem().getPrice()))             p.sendMessage(ChatColor.GOLD + "String_Node_Str" + getSelectedItem().getAmount()+ "String_Node_Str"+ f.format(getSelectedItem().getPrice())+ "String_Node_Str");
 else             p.sendMessage(ChatColor.GOLD + "String_Node_Str");
          }
 else {
            p.sendMessage(ChatColor.GOLD + "String_Node_Str" + f.format(getSelectedItem().getPrice())+ "String_Node_Str");
            p.sendMessage(ChatColor.GOLD + "String_Node_Str");
            setClickedSlot(event.getSlot());
          }
        }
      }
    }
 else     if (equalsTraderStatus(TraderStatus.PLAYER_SELL_AMOUNT)) {
      if (!event.getCurrentItem().getType().equals(Material.AIR)) {
        if (getClickedSlot() == event.getSlot()) {
          if (buyTransaction(p,getSelectedItem().getPrice(event.getSlot())))           p.sendMessage(ChatColor.GOLD + "String_Node_Str" + getSelectedItem().getAmount(event.getSlot())+ "String_Node_Str"+ f.format(getSelectedItem().getPrice(event.getSlot()))+ "String_Node_Str");
 else           p.sendMessage(ChatColor.GOLD + "String_Node_Str");
        }
 else {
          p.sendMessage(ChatColor.GOLD + "String_Node_Str" + f.format(getSelectedItem().getPrice(event.getSlot()))+ "String_Node_Str");
          p.sendMessage(ChatColor.GOLD + "String_Node_Str");
          setClickedSlot(event.getSlot());
        }
      }
    }
 else     if (equalsTraderStatus(TraderStatus.PLAYER_BUY)) {
      if (selectItem(event.getSlot(),TraderStatus.PLAYER_BUY).hasSelectedItem()) {
        p.sendMessage(ChatColor.GOLD + "String_Node_Str" + f.format(getSelectedItem().getPrice() * event.getCurrentItem().getAmount())+ "String_Node_Str");
      }
    }
    setInventoryClicked(true);
  }
 else {
    if (equalsTraderStatus(TraderStatus.PLAYER_BUY)) {
      if (selectItem(event.getCurrentItem(),TraderStatus.PLAYER_BUY,true,false).hasSelectedItem()) {
        if (getClickedSlot() == event.getSlot() && !getInventoryClicked()) {
          if (sellTransaction(p,getSelectedItem().getPrice(event.getSlot())))           p.sendMessage(ChatColor.GOLD + "String_Node_Str" + event.getCurrentItem().getAmount()+ "String_Node_Str"+ f.format(getSelectedItem().getPrice() * event.getCurrentItem().getAmount())+ "String_Node_Str");
 else           p.sendMessage(ChatColor.GOLD + "String_Node_Str");
        }
 else {
          p.sendMessage(ChatColor.GOLD + "String_Node_Str" + f.format(getSelectedItem().getPrice() * event.getCurrentItem().getAmount())+ "String_Node_Str");
          p.sendMessage(ChatColor.GOLD + "String_Node_Str");
          setClickedSlot(event.getSlot());
        }
      }
    }
 else     if (selectItem(event.getCurrentItem(),TraderStatus.PLAYER_BUY,true,false).hasSelectedItem()) {
      if (getClickedSlot() == event.getSlot() && !getInventoryClicked()) {
        if (sellTransaction(p,getSelectedItem().getPrice(event.getSlot())))         p.sendMessage(ChatColor.GOLD + "String_Node_Str" + event.getCurrentItem().getAmount()+ "String_Node_Str"+ f.format(getSelectedItem().getPrice() * event.getCurrentItem().getAmount())+ "String_Node_Str");
 else         p.sendMessage(ChatColor.GOLD + "String_Node_Str");
      }
 else {
        if (!event.getCurrentItem().equals(new ItemStack(Material.WOOL,1,(short)0,(byte)3)) && !event.getCurrentItem().getType().equals(Material.AIR)) {
          p.sendMessage(ChatColor.GOLD + "String_Node_Str" + f.format(getSelectedItem().getPrice() * event.getCurrentItem().getAmount())+ "String_Node_Str");
          p.sendMessage(ChatColor.GOLD + "String_Node_Str");
          setClickedSlot(event.getSlot());
        }
      }
    }
    setInventoryClicked(false);
  }
  event.setCancelled(true);
}