The shield is supposed to only affect melee attacks, and probably only enemy attacks as well.
1. have a party member equip Sura's Copper Plate
2. cast any of cipher's abilities on said party member
3. cipher receives dmg
As far as I know it's only affecting cipher's abilities atm. It's quite annoying because Pain Block is a really good buf that provides DR but it kills my Griveous Mother...
See the combat log(i casted blindstrike because you can't cast party buffs ooc) you see that after the first miss eder retaliates. I assume the retaliation uses the main weapon as Eder has a stilleto equipped.