According to itemDB, the weapon "Blue Steel Sword" is supposed to grant 2 points of hyperborean resistance. It has the line "<resistbuff hyperborean="2" />" but the tooltip displays a blank line instead of a resistance. When you wield the sword, your resistance do not change. I was just holding one a few minutes ago, so I'm absolutely certain it's not working, at least on my Mac. Timberbane is likewise supposed to give three slashing resistance, but I don't believe it did so the last time I was using one (a few days ago, so I can't be 100% certain). I've never held a Magma Mace, but since it uses the same line of code, I'm guessing it's not gonna work either. I can also confirm that modded weapons that use a resistbuff line do not impact your resistances. Trying to debug one of my modded weapons was actually how I noticed the problem in the first place. As with the blue steel sword, any modded weapon with a resistbuff just gets a blank line inserted between the damage section and the other buffs of the tool tip. EDIT: To be clear, resistances granted to weapons via Krong, Evil Chests, etc are working fine. My character that was wielding a Blue Steel Sword was also holding an artifact weapon that randomly had two righteous resist, and those righteous worked just fine.
Found another one, though this is a variation on the pattern above. Malleus Maleficarium has <resistbuff acidic="8" righteous="-8"/>, but only the righteous penalty ever shows up. I had two copies of it in my inventory in a game yesterday, and neither one displayed the acid resist.
To add to this, trying to create an item with resistances doesn't work either. Had some on a sword I made and none of them showed up.
Yes, as mentioned in my first post, that was how I first discovered the bug. I made several new weapons for Interior Dredmorating, and was shocked when I noticed that the three that had resistances built in weren't working as expected. I'd copied their code direct from the Blue Steel Sword, and just changed the damage types, so they ought to work.
Perhaps I should make a new thread for this, because it's not exactly the same bug as the others, but it's still in the category of items in the game not doing the things they're coded to do. playerHitEffectBuff does not appear to work on neck armor. I was just testing it on a new amulet I made, and despite basically letting a zoo pound on me with my very flashy feathered boa set for percentage="100", it never triggered once. I've verified my code, and can't find anything wrong with it. So I double-checked the files in Realm of the Diggle Gods, and saw that <playerHitEffectBuff percentage="50" name="Weak Spiky Hit" /> is used on the Spiked Leather Collar. I can't say that I recall it ever triggering, either, though I suppose it could just be subtle. Still, I think there's a very good chance that playerHitEffectBuff is not working with amulets/neck armour, which bugs/disables an existing piece of equipment, and limits modding options.