I went to the East Brit provisioner this evening to sell some stuff. I sold all of my items to the provisioner and she purchased the hot sell bag itself in the last batch of items. I've used my hot sell agent many times before and this has never happened.
Are you sure you didn't unintentionally set the hot-bag itself as an item listed in the Sell Agent? I am fairly certain that provisioners will buy backpacks, bags & pouches since they offer to sell them as part of their standard wares, I can't think of any other reason why this would have happened though.