I've experienced this issue on Definitive Edition v3.6.64.2709 running in Windows 10 Pro Version 1903 (OS Build 18362.836).
Bug description: When right clicking and choosing to "Equip" an item from a character's corpse that they had equipped, it can be swapped with your currently equipped item. The corpse will equip your original item as a result, but the exchanged item will not appear in the corpse's inventory. It will appear on their model as though they have it equipped, and it cannot be retrieved through any means (that I've found). Saving and reloading does not cause the item to become lootable. As far as I can tell, the item is lost forever. I lost about an hour of progress to this bug as a result of losing my best weapon permanently.
Steps to reproduce: I've only managed to reproduce this bug with one specific character (The Red Prince, who is also my Party Leader). I simply interact with the character corpse (in this case, Dorian Gall at the termination of his quest in his laboratory, after choosing to kill him) and equip his wand from the loot window. Any item I equip on The Red Prince beforehand will be swapped on the corpse in the manner described above. This does not happen with any other character in the party.