Yesterday I had a fight in Szarr's palace which involved also a kind of werewolf. They are from the description immune to all physical damage. I had three casters and only Jaheira as Fighter, so not much of a problem. To the end of the fight I had one weapon throw of Jaheira left without good use, so I moved her to the remaining werewolf. I thought that at least the necrotic damage (it's the Sword of Chaos) would apply, better a bit than nothing. I was quite surprised that it also dealt the full 20 physical damage of the damage roll.

Is this a bug? Or do physical weapons which also have elemental damage overcome physical immunity?