I'm in the habit of filtering with '(' upon attempting to wield a weapon, to make the process quicker. A few minutes after killing the minotaur emperor I felt like wielding his axe, only to find that it wasn't anywhere in my inventory. I actually back-tracked to his level and killed enemies looking for it! Turned out it was there all along but when I filtered the items, it made some of them disappear. That is, the last six or so two-handed weapons could only be seen when not filtering.