InventoryClickEvent срабатывает через раз

import org.bukkit.Material; 
import org.bukkit.event.inventory.InventoryClickEvent; 
import org.bukkit.event.player.PlayerDropItemEvent; 
import org.bukkit.event.EventHandler; 
import org.bukkit.event.EventPriority; 
 
import org.bukkit.entity.Player; 
import org.bukkit.inventory.ItemStack; 
 
public class Handler implements org.bukkit.event.Listener { 
     
    @EventHandler(priority = EventPriority.HIGHEST) 
    public void onInventoryClick(InventoryClickEvent event) 
    { 
        Player player = ((Player)event.getWhoClicked()); 
         
        ItemStack currentItem = event.getCurrentItem(); 
              
        if(currentItem == null || currentItem.getType() != Material.BOOK) return; 
         
        event.setCancelled(true); 
	player.updateInventory(); 
    } 
     
    @EventHandler 
    public void onDropItem(PlayerDropItemEvent event) 
    { 
        if(event.getItemDrop().getItemStack().getType() != Material.BOOK) return; 
         
        event.setCancelled(true); 
    } 
}