I think that when it got changed so that meeles wouldnt have stacking issues, it created stacking issues for casters.
This is really obnoxious, and makes it not even worth using vah back anytime but the very end of the fight, since if I use it early, I lose 20% damage from cunning for the remainder. I also keep just clicking the thing and getting it blocked because I am not used to having to click cunning.