Is GetItemCraftingInfo limited or buggy?

[thifi]

Hi,

I'm trying to query an item's crafting info inside an addon I'm developing and I'm getting strange results.

For a lot of items GetItemCraftingInfo returns valid values, but for a lot, the returned results are 0.

Example:
- link: [[|H2DC50E:item:45052:19:4:26844:19:4:0:0:0:0:0:0:0:0:0:4:0:0:63:0|h[maple restoration staff of shock^n]|h]]
- returned TradeSkillType = 0
- returned ItemType = 0

I found a lot of items like this in my char's inventory, sample code snippet to prove it:

...
local x,y = GetItemCraftingInfo(bagId, slotIdx)
local z = GetItemType(bagId, slotIdx)

if (y ~= z) then
    debug(colYellow .. "Item: " .. temName .. ", x: " .. x .. ", y: " .. y .. ", z: " .. z)
else
    debug(colGreen .. "Item: " .. itemName .. ", x: " .. x .. ", y: " .. y .. ", z: " .. z)
end
...

Is this a bug or a limitation?