Found another bug linked to wearing the Zombie Dragon ancient costume.
Apart from not being able to add to hoard while wearing one.

When crafting with a full disc and pet, you turn the raw material (this was crimson azulyte) into focused and it all goes into your back pack as normal making you over weight, but you cannot put processed resources into pet or disk.
Tried with just 1 piece and still not.
Looks like this is a sort of "cannot add to containers while wearing a costume" type of bug.