OnDispenserBonus being triggered twice

Code:

 object OnDispenserBonus(ResourceDispenser dispenser, BasePlayer player, Item item)
        {
            if (player.IsAdmin)
                Puts("OnDispenserBonus works!");
            return null;
        }

(21:14:30) | [TestPlugin] OnDispenserBonus works!
(21:14:30) | [TestPlugin] OnDispenserBonus works!

I tested stone, sulfur and metal nodes. It seems that whenever you trigger the finishing bonus on a metal node, the hook is called twice. I was using a salvaged pick. Trees seem to be OK.

Oxide issue? Game bug? Something I goofed?