One final thing, this bug does not apply with % Damage to Demons and % Damage to Undead:
Originally Posted by Fabian
I have mine socketed with a rare Jewel with the Diamond affix (+ED and AR against Demons), and some other helpful stuff. Damage, regular ED, stats, resists, it's all good. Do note that the bug with %ED and +damage in a jewel socketed in a non-weapon does NOT exist when that %ED comes in the Diamond or Pearl prefix. Ragnarod tested this for me (thanks!), and these jewels work as they should.
I've just done some quick tests of my own to corroborate this.