(Very minor spoiler warning)
I found a Minor Ring of Protection in Easternwood (in a hidden brick in the graveyard), and I tried to put it on Eder.... It didn't do anything. I put it on my main character, and it increased two of the three stats it was supposed to affect. I put it on another character, and it increased all three stats. It appeared to increase stats that were below 50, but have no effect on stats above 50.
I've attached two screenshots of my attempt to have Eder wear it. The first one shows the infobox for the ring, while it's in Eder's inventory (you can see it just to the right of the infobox):
Ring_of_Protection.jpg 152.95KB 0 downloads
The scond one shows the ring on Eder:
Ring_of_Protection_worn.jpg 128.57KB 0 downloads
In both screenshots, you'll see that his Fortitude, Reflex, and Will are 70, 50, and 50. The ring should increase them to 75, 55, and 55.
As the subject says, I'm using Steam version 1.0.6.0591.