See:
https://forum-en.gw2archive.eu/forum/community/api/Ghastly-Grinning-Shield-in-API/6630945
The vendor value of item 36332 is 0, which AFAIK makes the item implicitly untradeable. I believe the API is correct (and attempts to purchase it via the TP should fail, regardless of what the UI displays).
There are some additional player comments in the thread, but no further follow-up from the developer. It’s unclear from reading whether it’s the shield that’s bugged or the other ‘grinning weapons’ that are bugged. All we (as players) can really say is that it’s inconsistent.
John Smith: “you should kill monsters, because killing monsters is awesome.”