Mind Fog question

[Cheiromancer]

The text of mind fog says

Mind fog produces a bank of thin mist that weakens the mental resistance of those caught in it. Creatures in the mind fog take a -10 competence penalty on Wisdom checks and Will saves. (A creature that successfully saves against the fog is not affected and need not make further saves even if it remains in the fog.) Affected creatures take the penalty for as long as they remain in the fog and for 2d6 rounds thereafter...

Now, mind fog allows a will save to negate it. My question is: Suppose a character enters into an existing mind fog. Does the -10 penalty apply to the initial will save? I had thought that the answer would be "no" but now I am not too sure. After all, in the explanatory text "A creature that successfully saves against the fog is not affected" the expression "is not" is ambiguous. Does it mean "A creature that successfully saves against the fog is no longer affected" (i.e. it took the penalty for that initial save) or "A creature that successfully saves against the fog was not affected"? (i.e. it did not take the penalty for the initial save). But the second option would seem to make the effect of the saving throw retroactive.

If the spell were cast around the character, the save would be without a penalty. But if the character walks into its area of effect, the mind fog is an existing condition, and it should have its normal effects until a saving throw overrides it. But that means the character's saving throw will be at a -10 penalty.

What do other people think?

 

[Jack Simth]

Make the save with no penalty; penalty only applies after the save fails. Otherwise it's a tad too powerful for my tastes.

 

[Infiniti2000]

When a spell says Will negates, then you roll the saving throw before applying the spell effects to the targets. You do not apply the modifier to the saving throw vs. the spell itself.