On dungeon level 10 I picked up a suit of crummy artifact armor (a variant of embossed serpentine plate), which I meant to send to the museum for experience. However, I accidentally selected the skill Lucky Pick instead of It Belongs in a Museum. When I right-clicked on the crummy armor, it switched with the nice armor I had been wearing (as normally happens when right-clicking a wearable inventory item). The nice armor, though, didn't appear in my inventory or on the ground; instead it totally vanished. My inventory was full at the time, which may have been a contributing factor. Snow Leopard, Steam, 1.0.10, RTDG, no mods.