When you right click a lectern with a book the resulting event contains
the player and the item.
Both the event.getItem() and the player.getInv.getIteminMainHand return an interesting item
the handle is clearly correct -CraftItem - in the test case a book
however the item.getType = AIR and the amount = 0

I have attached a snippet from a debug session the code used to retrieve the data is

    @EventHandler(priority = EventPriority.MONITOR, ignoreCancelled = true)
    private void playerInteractEventMonitor(PlayerInteractEvent event) {

        final Player player = event.getPlayer();
        Block block = event.getClickedBlock();
        ItemStack hand = player.getInventory().getItemInMainHand();
        ItemStack item = event.getItem();

This was replicated while testing an implementation of my logging plugin Prism-Bukkit,
It was the only plugin installed.