Fortify Pickpocket potions and items with the Fortify Pickpocket effect not only don't work, they have the opposite effect.

For example, if I use a Fortify Pickpocket 20% potion then my chance to pickpocket will be REDUCED by 20%. Anybody with Fortify Pickpocket gear on will notice their pickpocket chance go up when they remove their gear.

Hmmm.. I found a fort pickpocket amulet early in my character's adventure, and have used it occasionally as I'm not a thief in general, even took notice that it did actually give a better %chance when pickpocketing. Perhaps there's something that triggers this?

I don't know. I've only tested it with gold because it's the only thing I can get valuable enough to lower my pickpocket chance below 90%. Maybe it has to to with the 50% easier chance to pickpocket gold perk which I have.