this happened to me while in Spellhold. The party entered the second level (where the kobolds and the vampire are) and I suddenly noticed that the Free Action buff from Keldorn is missing. I couldn't figure why so I started to check his stuff to see which item provides this bonus - and to my astonishment, he wasn't wearing his breastplate! There he was, stark naked in 10 AC, and I found his stuff dropped on the ground nearby. At this time I thought it might have been a misclick (although I was pretty sure that I had not open the inventory since I had entered this level) so I went on. However, another fight later I noticed that the level drain buff is missing from Viconia, too! I instantly checked her bags and he was indeed missing the amulet that gave protection against energy drain. I had to walk back and comb the place to find it lying on the ground!
Although I have found the missing items I still don't understand how they got dropped. I'm absolutely sure that I didn't remove them on purpose, and even if everyone's bags had been full when I recieved something, these items couldn't have been removed automatically because they were worn (placed in the slots on the paper dolls). Any idea?
