If a jewel gives +to minimum damage, +to maximum damage, or both with ed% on them, it will bug if it is not in your weapon slot.
For instance, if I put on a 40%/15 max jewel. Say I wanna throw that in my helm. What will happen is, I gain 15 max damage and 40% increased minimum damage. Or vice versa. if I have a rare jewel with say, 30% ED/9 max/4 min and put it in my helm, it has 0 effect at all. It's a weird thing with jewels. If you were to put that same 40%/15 max in your weapon, however, it would work perfectly fine.