No, they don't, which is really stupid. I managed to one-hit an Adamantine with a Vorpal Sword, too. The chances of that happening are one in about twenty, so it's not exactly a super reliable method of dealing with them. Sanctuary is a greatly underestimated spell; a little known fact is that clerics can cast healing spells while sanctuaried. Bloody drow cleric did it to me in that fighting pit in Ust Natha.
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