While Wish-Ender is equipped putting on Piercing Bowstring and then taking it off strips the weapon it of its intrinsic Anti-Barrier properties. Same thing with Malfeasance and the Unstoppable HC mod. This bug has been in the game since last season, when equipping the Overload bow mod would override Wish-Ender's Anti-Barrier capabilities. On a side note, as many people have pointed out before, the Unstoppable HC mod takes way too long to proc.