Help with understanding PutItemInBag(23)

[pasiv]

I'm new to lua, and I'm trying to make a tiny addon for myself that will help me manage my inventory. I'm currently trying to move items from inventory to a free bag slot, but in my testing, it seems that "PutItemInBag(23)" is not functioning at all as I had expected. "PutItemInBackpack()" works perfectly fine. So what am I missing here?

PickupInventoryItem(GetInventorySlotInfo("HEADSLOT"))
if CursorHasItem() then
   --PutItemInBackpack() -- Works fine.
   PutItemInBag(23) --! Doesn't work on beta or live, but works in wrath.
end

Forgive my noobishness, I'm super green.