I did some testing with my party of drow/deep gnomes -- Holy Aura spell takes them up to the max Spell Reistance of 50, which in theory makes them immune to their own spells. I tried skull trap, cone of cold, acid storm, DBF, horrid wilting, meteor swarm, and M.'s Force Missiles. This was in HoF, if it matters.

Cone of cold, horrid wilting, and meteor swarm always completely ignored spell resistance. In my opinion, that counts as a bug.

(Side note on meteor swarm: It has a duration of one round; a character who is not in the AOE when the spell is cast, but moves in before the six seconds are up, will be damaged. However, it can only damage each character once, even if he leaves and returns to the AOE several times.)

The other spells were almost always foiled by spell resistance, _but_ if I could force several spell resistance checks at nearly the same time, sometimes a spell would go through, even though it shouldn't.

Example: all three characters clustered together. two of them cast skull trap at each other simultaneously. Rarely, one character will be damaged by one skull trap.

Easier example: cast a bunch (6+) of skull traps or DBFs close together. Walk a character into them; he will resist some and be damaged by some.

According to spiffy 3E rules, when a caster casts a spell at a spell-resistant foe, he makes a caster level check. This is 1d20+CasterLevel, if the result is equal or higher than the target's SR, spell effects normally. There is a feat called Spell Penetration which gives +2 bonus and can be taken twice for a total of +4 bonus.

So a 30th level caster with Greater Spell Penetration will roll 1d20+34 to penetrate the victim's SR. In your example, if your mages are HIGH level, they can SOMEHOW penetrate 50 SR and their spells work normally.

^WHY, in above example the arch-mage needs to roll a 16 on 1d20, it is HARD but not impossible as you can see with %25 chance of success. Maybe this is your answer, I am not sure though. What was your mage's levels? Did they have Spell Penetration Feat?

None of my characters have any Spell Penetration, and none of them are level 30. I did make sure of that before testing...

Is it possible a natural 20 punches through Spell Resistance, like a nat 20 is an auto hit?

^CLEVER! Yes it may be the cause, not sure though.

A nat 20 _shouldn't penetrate spell resistance, but even if it does, that is not what I am seeing.

To repeat:

Cast skull traps at a highly spell resistant character at intervals. He will resist them all.

Cast a whole bunch of skull traps on top of each other, and then walk into them. About half of them will penetrate his spell resistance, even though he should be immune.

Strange then, can you abuse it to your liking?

I like to have all my characters be drow or deep gnomes; these bugs mean that I'm getting less mileage than I should out of my SR.

Hmmmm... are the bugs abusable, assuming they work the same way against enemies with SR as they do against my SR characters? Let's pretend I don't want to cast Lower Resistance.

So now we know to use Cone of Cold, Horrid Wilting, and Meteor Swarm against SR. But we were probably already using those spells, especially the latter two.

And we know that a big pile of skull traps and DBFs sometimes beat SR when they shouldn't. But if you have time to set a trap like that, you have time to cast LR.

So basically this bug hurts you a lot more than it helps you.

let me throw a theory at you, its spell resistance, some is innate and some isn't ... some require certain classes meaning those classes had to study on ways to resist magic.

The non-innate resistance requires focusing to resist the spell, thus, when its only one or a few spells, you can resist it, but when barraged (spelling?) by spells, its harder to focus and you can't resist them all...

now, i'm not sure if its intentionally made this way but it CAN be explained by simple theory...use some imagination ^_^