nAre hidden appareances not saved aymore in 9.1?

[sezz]

I'm not sure if this is this a 9.1 bug or an issue on my side:

"Hidden Chestpiece", "Hidden Cloak" and others don't enable the "Save" button anymore in the wardrobe + they aren't saved on the server.

Is there an ID for those hidden appearances to force saving?
So far I only found Constants.Transmog.NoTransmogID but that's not the correct one.