(a) Unless the warehouse receipt otherwise provides, a warehouse shall keep separate the goods covered by each receipt so as to permit at all times identification and delivery of those goods. However, different lots of fungible goods may be commingled.

(b) If different lots of fungible goods are commingled, the goods are owned in common by the persons entitled thereto and the warehouse is severally liable to each owner for that owner's share. If, because of overissue, a mass of fungible goods is insufficient to meet all the receipts which the warehouse has issued against it, the persons entitled include all holders to which overissued receipts have been duly negotiated.