Program: 169582
Project: 169582
Buggy source:
@Override public boolean onItemUse(ItemStack stack,EntityPlayer player,World world,int x,int y,int z,int side,float hit_x,float hit_y,float hit_z){
  if (player != null && stack != null && stack.getItem() == this) {
    if (world.isRemote) {
      return true;
    }
    final Location location=new Location(world,x,y,z);
    TileEntity tile=location.getTileEntity();
    if (tile instanceof IMultiTile) {
      IMultiTileHost host=((IMultiTile)tile).getHost();
      if (host instanceof TileEntity) {
        tile=(TileEntity)host;
      }
    }
    if (player.isSneaking()) {
      Location storedLocation=getLocation(stack);
      if (storedLocation != null && storedLocation.equals(location)) {
        LanguageUtility.addChatToPlayer(player,"String_Node_Str");
        return true;
      }
      setLocation(stack,location);
      LanguageUtility.addChatToPlayer(player,"String_Node_Str");
      if (tile instanceof IPassCode) {
        setCode(stack,((IPassCode)tile).getCode());
      }
      stack.setItemDamage(1);
      player.inventoryContainer.detectAndSendChanges();
      return true;
    }
 else {
      Location storedLocation=getLocation(stack);
      if (storedLocation != null) {
        if (!storedLocation.equals(location)) {
          if (!storedLocation.isAboveBedrock()) {
            LanguageUtility.addChatToPlayer(player,"String_Node_Str");
            return true;
          }
 else           if (tile instanceof ILinkable) {
            String result=((ILinkable)tile).link(storedLocation,getCode(stack));
            if (result != null && !result.isEmpty()) {
              if (result.contains("String_Node_Str")) {
                String translation=LanguageUtility.getLocalName(result);
                if (translation == null || translation.isEmpty()) {
                  translation="String_Node_Str";
                }
                player.addChatComponentMessage(new ChatComponentText(TextColor.RED.getColorString() + translation));
              }
 else {
                LanguageUtility.addChatToPlayer(player,result);
              }
            }
 else {
              LanguageUtility.addChatToPlayer(player,"String_Node_Str");
            }
            return true;
          }
 else {
            LanguageUtility.addChatToPlayer(player,"String_Node_Str");
            return true;
          }
        }
 else {
          LanguageUtility.addChatToPlayer(player,"String_Node_Str");
          return true;
        }
      }
 else {
        LanguageUtility.addChatToPlayer(player,"String_Node_Str");
        return true;
      }
    }
  }
  return false;
}

Fixed version (ground truth):
@Override public boolean onItemUse(ItemStack stack,EntityPlayer player,World world,int x,int y,int z,int side,float hit_x,float hit_y,float hit_z){
  if (player != null && stack != null && stack.getItem() == this) {
    if (world.isRemote) {
      return true;
    }
    final Location location=new Location(world,x,y,z);
    TileEntity tile=location.getTileEntity();
    if (tile instanceof IMultiTile) {
      IMultiTileHost host=((IMultiTile)tile).getHost();
      if (host instanceof TileEntity) {
        tile=(TileEntity)host;
      }
    }
    if (player.isSneaking()) {
      Location storedLocation=getLocation(stack);
      if (storedLocation != null && storedLocation.equals(location)) {
        LanguageUtility.addChatToPlayer(player,"String_Node_Str");
        return true;
      }
      setLocation(stack,location);
      LanguageUtility.addChatToPlayer(player,"String_Node_Str");
      if (tile instanceof IPassCode) {
        setCode(stack,((IPassCode)tile).getCode());
      }
 else       if (tile instanceof ITileNodeHost && ((ITileNodeHost)tile).getTileNode() instanceof IPassCode) {
        setCode(stack,((IPassCode)((ITileNodeHost)tile).getTileNode()).getCode());
      }
      stack.setItemDamage(1);
      player.inventoryContainer.detectAndSendChanges();
      return true;
    }
 else {
      Location storedLocation=getLocation(stack);
      if (storedLocation != null) {
        if (!storedLocation.equals(location)) {
          if (!storedLocation.isAboveBedrock()) {
            LanguageUtility.addChatToPlayer(player,"String_Node_Str");
            return true;
          }
 else           if (tile instanceof ILinkable) {
            String result=((ILinkable)tile).link(storedLocation,getCode(stack));
            if (result != null && !result.isEmpty()) {
              if (result.contains("String_Node_Str")) {
                String translation=LanguageUtility.getLocalName(result);
                if (translation == null || translation.isEmpty()) {
                  translation="String_Node_Str";
                }
                player.addChatComponentMessage(new ChatComponentText(TextColor.RED.getColorString() + translation));
              }
 else {
                LanguageUtility.addChatToPlayer(player,result);
              }
            }
 else {
              LanguageUtility.addChatToPlayer(player,"String_Node_Str");
            }
            return true;
          }
 else {
            LanguageUtility.addChatToPlayer(player,"String_Node_Str");
            return true;
          }
        }
 else {
          LanguageUtility.addChatToPlayer(player,"String_Node_Str");
          return true;
        }
      }
 else {
        LanguageUtility.addChatToPlayer(player,"String_Node_Str");
        return true;
      }
    }
  }
  return false;
}