There are some oddities with how monster inventories work.
There are some oddities with how monster inventories work as of version 1.1.1. While if I remember correctly, that's still an underdeveloped feature of the game, I believe there are some issues which should be fixed - those are:
1. Suffocated monsters don't drop items.
2. Humanoids equipping two shields can still melee the player.
3. Dragons and wyrms can equip human-sized gear.
4. Monsters can have negative DV from equipping armor and such, whereas the PC always has at least 1 DV.
5. Items given to monsters by the level 40 merchant class power, money paid to Skriek, and wedding rings 'g'iven to berserkers, don't go to the monsters' inventory.
6. Monsters equipping weapons still keep their normal damage (according a blessed stethoscope), while still getting DV and PV bonuses from the weapon, if any.
1. Make suffocated monsters drop items.
2. Only allow monsters to equip one weapon and one shield.
3. Only allow monsters with the "humanoid" flag to equip items.
4. Make the minimum DV for monsters 1.
5. Make those items to to the monster's inventory.
6. Replace the damage die of the monster with that of the newly-equipped weapon. Combined with point 2, there are no concerns about two weapon combat.
Imo money paid to Skriek should disappear, that is not a bug. If it doesn't, you can easily get a complete key set for free. You just buy the keys and slay him. It stands to reason that Skriek spends the money he earns.
There is something to be said for the other items disappearing too, actually. Monsters could refuse chaos orbs if a merchant tries to give them away.
edit: The other oddities are actually better kept as well imho, just to keep things simple. For example, if equipping weapons is going to change the damage a monster does, they need to make intelligent decisions about what to equip. Unless you would like to see balors eliminated by letting them equip dual shields or a corroded cursed broken fickle orc knife of doom.
^ Valid points. Maybe "bugs" wasn't the best word, I'm just exposing behavior which I believe might not be intended.
As for cursed broken orcish knives, letting monsters pick up gauntlets of peace is already a good way to ID them :) Maybe not all of them would be able or wanting to equip weapons, depending on their intelligence. Although that kind of decision-making is probably something for ADOM II.