- Markshire PCs: Grottle, Gruzk, Ashimar
The ability points stacking are a known glitch in NWN.
As Mule states, in PnP the rule for stacking is they don’t, except for Dodge.
As to the mithril issue, the damage afforded by the Mithril is Slashing which is essentially the same damage afforded by the plus given by the spell. +5 straight is better then a die roll and therefore overrides the slashing damage.
Now, is this a glitch? No idea. Personally, I feel the two should work separately.
What I feel and what I can do to resolve this are two separate issues, of course. There is no recourse for changing this.