Program: 79968
Project: 79968
Buggy source:
@EventHandler(priority=EventPriority.HIGH) public void onInteract(PlayerInteractEvent e){
  if (e.getAction() != Action.RIGHT_CLICK_BLOCK)   return;
  Block b=e.getClickedBlock();
  SlimefunItem item=BlockStorage.check(b);
  if (item != null) {
    if (item.getName().equals("String_Node_Str")) {
      e.setCancelled(true);
      Item stack=findItem(b);
      if (stack == null) {
        insertItem(e.getPlayer(),b);
      }
 else       if (!removed_items.contains(stack.getUniqueId())) {
        final UUID uuid=stack.getUniqueId();
        removed_items.add(uuid);
        SlimefunStartup.instance.getServer().getScheduler().scheduleSyncDelayedTask(SlimefunStartup.instance,new Runnable(){
          @Override public void run(){
            removed_items.remove(uuid);
          }
        }
,30L);
        stack.remove();
        e.getPlayer().getInventory().addItem(fixItemStack(stack.getItemStack(),stack.getCustomName()));
        e.getPlayer().playSound(b.getLocation(),Sound.ENTITY_ITEM_PICKUP,1F,1F);
        PlayerInventory.update(e.getPlayer());
      }
    }
 else     if (item.getName().equals("String_Node_Str")) {
      e.setCancelled(true);
      ItemStack catalyst=e.getPlayer().getInventory().getItemInMainHand();
      List<Block> pedestals=Pedestals.getPedestals(b);
      if (!altars.contains(e.getClickedBlock())) {
        altars.add(e.getClickedBlock());
        if (pedestals.size() == 8) {
          if (catalyst != null && !catalyst.getType().equals(Material.AIR)) {
            List<ItemStack> input=new ArrayList<ItemStack>();
            for (            Block pedestal : pedestals) {
              Item stack=findItem(pedestal);
              if (stack != null)               input.add(fixItemStack(stack.getItemStack(),stack.getCustomName()));
            }
            ItemStack result=Pedestals.getRecipeOutput(catalyst,input);
            if (result != null) {
              List<ItemStack> consumed=new ArrayList<ItemStack>();
              consumed.add(catalyst);
              PlayerInventory.consumeItemInHand(e.getPlayer());
              Bukkit.getScheduler().scheduleSyncDelayedTask(SlimefunStartup.instance,new RitualAnimation(altars,b,b.getLocation().add(0.5,1.3,0.5),result,pedestals,consumed),10L);
            }
 else {
              altars.remove(e.getClickedBlock());
              Messages.local.sendTranslation(e.getPlayer(),"String_Node_Str",true);
            }
          }
 else {
            altars.remove(e.getClickedBlock());
            Messages.local.sendTranslation(e.getPlayer(),"String_Node_Str",true);
          }
        }
 else {
          altars.remove(e.getClickedBlock());
          Messages.local.sendTranslation(e.getPlayer(),"String_Node_Str",true,new Variable("String_Node_Str",String.valueOf(pedestals.size())));
        }
      }
    }
  }
}

Fixed version (ground truth):
@EventHandler(priority=EventPriority.HIGH) public void onInteract(PlayerInteractEvent e){
  if (e.getAction() != Action.RIGHT_CLICK_BLOCK)   return;
  Block b=e.getClickedBlock();
  SlimefunItem item=BlockStorage.check(b);
  if (item != null) {
    if (item.getName().equals("String_Node_Str")) {
      e.setCancelled(true);
      Item stack=findItem(b);
      if (stack == null) {
        insertItem(e.getPlayer(),b);
      }
 else       if (!removed_items.contains(stack.getUniqueId())) {
        final UUID uuid=stack.getUniqueId();
        removed_items.add(uuid);
        SlimefunStartup.instance.getServer().getScheduler().scheduleSyncDelayedTask(SlimefunStartup.instance,new Runnable(){
          @Override public void run(){
            removed_items.remove(uuid);
          }
        }
,30L);
        stack.remove();
        e.getPlayer().getInventory().addItem(fixItemStack(stack.getItemStack(),stack.getCustomName()));
        e.getPlayer().playSound(b.getLocation(),Sound.ENTITY_ITEM_PICKUP,1F,1F);
        PlayerInventory.update(e.getPlayer());
      }
    }
 else     if (item.getName().equals("String_Node_Str")) {
      e.setCancelled(true);
      ItemStack catalyst=new CustomItem(e.getPlayer().getInventory().getItemInMainHand(),1);
      List<Block> pedestals=Pedestals.getPedestals(b);
      if (!altars.contains(e.getClickedBlock())) {
        altars.add(e.getClickedBlock());
        if (pedestals.size() == 8) {
          if (catalyst != null && !catalyst.getType().equals(Material.AIR)) {
            List<ItemStack> input=new ArrayList<ItemStack>();
            for (            Block pedestal : pedestals) {
              Item stack=findItem(pedestal);
              if (stack != null)               input.add(fixItemStack(stack.getItemStack(),stack.getCustomName()));
            }
            ItemStack result=Pedestals.getRecipeOutput(catalyst,input);
            if (result != null) {
              List<ItemStack> consumed=new ArrayList<ItemStack>();
              consumed.add(catalyst);
              PlayerInventory.consumeItemInHand(e.getPlayer());
              Bukkit.getScheduler().scheduleSyncDelayedTask(SlimefunStartup.instance,new RitualAnimation(altars,b,b.getLocation().add(0.5,1.3,0.5),result,pedestals,consumed),10L);
            }
 else {
              altars.remove(e.getClickedBlock());
              Messages.local.sendTranslation(e.getPlayer(),"String_Node_Str",true);
            }
          }
 else {
            altars.remove(e.getClickedBlock());
            Messages.local.sendTranslation(e.getPlayer(),"String_Node_Str",true);
          }
        }
 else {
          altars.remove(e.getClickedBlock());
          Messages.local.sendTranslation(e.getPlayer(),"String_Node_Str",true,new Variable("String_Node_Str",String.valueOf(pedestals.size())));
        }
      }
    }
  }
}