That was my first thought about the armor, but it wasn't replacing any armor: I picked it up and dropped it on an empty square.

I've since seen that effect once, so if either happens again, I'll nab the game and send it to you. And I'll make sure to grab a save of any interesting looking possibly-bug games.

The game shouldn't allow a res. and a vuln. to the same damage type on the same item. If that has happened then it is a bug. My initial thought is that the item got altered in play. The monster used an alter or similar. But it may also have been that the material of the cloak gave it a res. and then it got a vuln. in the enchantment process. Like I said though that shouldn't happen so I'll look into it.

The armour might be easier to explain though. Did the armour it replaced have the same range bonus? This would make it appear not to give you a bonus when it is put on.

If you still have the game saved I would be interested in taking a look at it - contact@gooeyblob.com

Another weird one: a breastplate that gives negative Ranged and Magic. But it apparently gave -0 Ranged, since it made no difference at all to my ranged stat (=51/14) if I picked it up and dropped it. It improves my defense, though, so I kept it.