I've raised this before, but didn't explain myself very well, and since I still think it's a problem...
As I understand it, one used to be able to sell bags/containers, but this functionality was removed, due to problems with accidentally selling bags full of goodies. And, as it turns out, I think the inability to sell bags works quite well, as it encourages people to recycle surplus bags to new players, or create treasure hunts etc.
But... the bags still suggest that they can be sold; on their info pages there are a 'Find auctions' links, and ghost auction pages; and the items all have a price, rather than "Vendors will not buy this item". So, when one tries to unsuccessfully sell a bag, it's frustrating, because it feels like it's broken. And thus I think the appearance of a bag's saleability is a bug.