Regarding the bug:
1. The last skill slot cannot be retrieved from the witch's hut. This is true for the 8th and 6th skills, depending on the game mode. Originates from ToE.
2. Originates from ToE. We used this as an opportunity to create a slightly different spell. It doesn't depend on luck, but to compensate, the spell deals significantly more damage. It's intended for hero builds without "Caster's Luck".
I would like to suggest reading the F.A.Q.