A question

[Karnor]

Is it possible to make SI (SI:Abj in particular) work properly? The spell description states that it should make the caster immune to both harmful and helpful spells of that class, not just harmful spells.

 

So SI:Abj should really remove the benefit of all those nice abjuration defensive spells, such as minor/major globe of invulnerability, mantle, etc. If a caster chooses to use it then they will effectively be self dispelling most of their own protections.

[Ardanis]

Seeing how SI:Abj does NOT protect from harmful antimagic spells, I see zero reason to block beneficial spells.

[DavidW]

Seeing how SI:Abj does NOT protect from harmful antimagic spells, I see zero reason to block beneficial spells.

 

You'll also break SCSII, most other mage AI I can think of, and the original game's AI. (It's completely clear that the designers intended SI:Abj to work this way.)