Yup, duplicates of the same item won't work, although there's what appears to be a bug with this for commanders capable of carrying more than 2 misc items.
Otherwise you'd never need to forge a treelord staff (2 thistle maces would be just as good) for example
Oh my. But commanders can only give that broth to so many troops per turn. I mean they cannot let those normal troops share that yummy broth because they cannot hold any misc items.