Just noticed this since I haven't tried it in a while, but I drank a 38% Restoration Potion, then went to equip my Ring of Restoration (15% discount), but it doesn't show the 38% increase like it used to....same with my Gaulder Amulet Fragment. It stays at +30 Magicka. Now, my spells are definitely effected by the potion.
I have the USKP, but this is not listed in the changelog. This wasn't fixed by 1.9 was it? I guess I'll just have to try to find a more powerful ring, then.