I think the issue is more extensive. I've been playing a character with spear as primary weapon, and have now lost 4 spears going through all current content. For me, the spear vanishes upon making a killing blow as a thrown shot, especially against LOX or trolls. I usually run up inside the dying beast to auto pickup any treasure, and to enjoy the view of the inside of the creature model. That usually recovers the spear as well. Maybe once in 50 kills the spear will have vanished. Just happened a few minutes ago, which is why I'm checking the chat.