The spell is grayed out and refuses to work. I tried resting, stripping him of his equipment, kicking him out the party and hiring him back, but so far nothing has worked for me. I'm afraid saving the game after the last fight has mad that condition permanent and the only other save game I've got is about 10 hours less than the recent one. That sucks big time! Is there any way to fix this?

I have the exact same problem. Answer would be appreciated.

Hey everybody, thank you for your feedback. The team is aware of this issue. We have a hunch that using an ability as a cutscene starts or as the game saves may cause it to remain in the activated state, but we are unsure if there are other ways this issue may arise. If anybody has any other ideas or 100% reproducible steps, it could help us pin-point the issue and find a solution. Thank you!

This is happening with my Mage as well. 

Please update as soon as a fix is reached, very frustrating.