Hexblade Curse + Knight Commander's Sabre Not Using Full AB

[PlunderBunny]

Description
==========
Was fiddling around with build and gear ideas on the PGCC, looking at a 25Hex/5Knight build using the Knight-Commander's Sabre. Tried using the Curse Weapon and noticed that my AB was not as high as I expected it would be, was 3 lower than where I thought. Compared the AB when using the Sabre to AB when using a standard Masterly Damask weapon and AB was where I expected it to be. The Knight-Commander's Sabre seems to be in the unique position of having both a +5AB and -3AB property applied to it simultaneously. So the -3 AB appears to be applying on top of everything, including any other enhancement bonuses a weapon might be able to become imbued with (i.e. Hexblade Curse Weapon, Blackguard Corrupt Weapon, Blade Thirst, etc.). I've only tested it with a Hexblade, but I'm guessing there are other similar abilities that would be effected by it too.

Steps to reproduce
----------------------------
Hexblade Curse check: Create character with Curse Weapon V who can use Knight-Commander's Sabre, equip Sabre and try to Curse, see whether AB is at the expected value.

Other weapon enhancement spell checks: Create character with appropriate build to use Knight-Commander's Sabre and imbue it with some enhancement, equip and imbue, see whether AB is at the expected value.

Expected result
-----------------------
At Curse Weapon V, would expect to be getting full +5 to attack bonus.

Actual result
-------------------
At Curse Weapon V, am only getting a total +2 to attack bonus.

Misc Notes
----------------
I'm by no means any kind of build/mechanical expert about either NWN or Arelith so maybe this is working exactly as was intended, but on the Wiki the Knight-Commander's Sabre is listed as having a +2 attack bonus, but is considered as +5 for the purposes of breaking DR. I assume that the two +5AB and -3AB properties applied to the weapon were the way of achieving this, but it seems to interfere with things that add an enhancement bonus to the weapon in a way that doesn't feel intended based on the description of the weapon on the Wiki. I don't know any of the under-the-hood details of how either the game or the server runs, but it feels like that interaction between enhancement bonuses and attack bonuses on that weapon isn't really how it's supposed to work. This might be a pretty niche case, but it feels like a bug to me all the same.

Which Server(s)?
------------------------
PGCC, have not tested on a live server

Gaming Platform(s)?
------------------------------
PC

[Scurvy Cur]

Fully consistent NWN behavior, and likely completely intended (Kenji might be able to chime in on this one to voice his intent for the item, but he's always had a pretty solid grasp on how item properties stack, so I assume he knew this was the result he'd get).

At issue here is how NWN treats stacking properties. The reason the KCS will penetrate DR is that the game does not actually ever combine the +5 AB and -3AB properties together to arrive at a +2 AB sword. Instead it sees a sword that simultaneously has a +5 AB property (allowing it to bypass /+5 soak DR) and a -3 AB penalty. When you add further properties, all of the default rules against stacking still apply. So when you add your curse, the game does not think you're adding a +5 enhancement bonus to a +2 AB weapon. It thinks you're adding a +5 enhancement bonus to a weapon with a +5 AB property, which will stack only with the damage component of your weapon curse.

By contrast, the largest single negative penalty to any stat on an item will stack. So what the game sees looks roughly like:

1) +5 AB
2) +5 Enhancement bonus, which can be expressed as:
2a) +5 AB which does not stack with the identical bonus from 1), and is therefore has no effect on your end AB
2b) +5 damage, which does stack
3) -3 AB, which stacks because it's a negative item property, rather than a positive one.

When the game is done parsing all of it, it just sees +5 ab from the base weapon, +5 damage from hexblade's curse, and -3 AB.

This is the result that ought to be expected and is, as far as I am aware, the intended final outcome.

[PlunderBunny]

Figured that was probably what was happening, thank you for confirming that I was thinking about it right! The thing is, it just feels strange, makes it feel like the weapon is actively hurting you in circumstances where it should be technically able to be better than the effective +2 AB that it has. So still curious to hear what Kenji might have to say about it!

[MRFTW]

Presumably, this will affect BG and Spellsword and their respective AB buffs, too.

[Kalopsia]

To my knowledge that's working as intended :)