From sorear: "When an item is marked as identifyable, such as a shop item or an ingot (if you pass a Metallurgy roll), the game identifies the class of items when they are stepped on. However, class identification will cause other ingots of the same type to become identified, and restacked; the restacking invalidates the initial identification's loop pointer, and things blow up. This also happens with Khelevastar (due to a bug, his spellbooks are sometimes marked as identifiable)"