Potions of fortitude do not seem to be applying any bonus to the fortitude save. I can confirm they are not working when someone stun fists you.
- Not.Him.Again
Potions of fortitude are potions of iron guts (+4 fort save bonus vs. poison only).
yes this is correct. +4 to poison save only.
There are a bunch of potions that don't have the name "potion of Spell X". Examine them and see what spells they cast. EfU has plenty of custom pots too. If you want Fort saves, use a potion of Endurance.
What they mean is your character sheet won't update unless the bonus is general. Like for example using Protection from Evil will not show a +2 ac in your character sheet even though the spell gives you +2 deflection. You still get it, it just doesn't show in the sheet. (And like they said, Fortitude potions cast "Ironguts" which are in fact +4 vs poison, not a general bonus)