Items may sometimes duplicate in the inventory and disappear upon relogging
It's not clear how to reproduce this bug exactly. I traded a set of tradesman's pride to get 4 unstable idols + 1 bone idol, then when I tried to drag that unstable stack around the inventory, a second stack appears (and can be further moved in the inventory) while the original stays in place. After relogging, both stacks are gone from the inventory.
It seems w0lly also encountered this bug.