Hello, I am experiencing something similar just with Concelhaut's Draining touch (https://pillarsofeternity.gamepedia.com/Concelhaut%27s_Draining_Touch).
It says that a the weapon is equipped and can't be unequipped. The tooltip reads as if it is a one time attack, but it seems to last indefinitely and I can't unequip the weapon.
I have tried retraining the character and it doesn't solve the issue. Any fixes would be awesome! Thanks.