Do you continually check on him while he has the item though? If you keep approaching him, even looking at him while he has the item, he will continue to guard it, and will get more and more anxious about it, because you have a history with him of removing things despite him telling you every way he knows how not to. So he is very worried. I bet if you truly ignore him, he will slowly learn to stress less. And when he does walk away, and you do remove whatever the item is, make sure he doesn't see you doing it.