I was using leveling my pickpocket skill via a trainer, paying them and then stealing back the gold. Eventually my chance of success got to be pretty low due to the amount of gold so I got a ring with a pickpocket %mod on it. When I put the ring on my chance of success went DOWN. The same thing happened with my smithing. I was trying to improve my Daedric Bow, with no mods it went to LEGENDARY with 143 damage. I put on a 20% smithing mod ring and it went DOWN to 126, I put on my 20% necklace as well and it dropped to just above 100. Are the mods broken or is there some hidden skill cap that going over it gives negative returns?
TL;DR: High skills = worse results. WTF?