Skill/Spirit assign for Demon form issue

You can not assign Spirit gems to demon form. For me the skills are greyed out and say "skill is not valid for this weapon set"

The skill is not being used on any other weapon set and I have the spirit but won't let me assign it.

With more testing I've been able to get Grim Feast working in demon form some how, although it's not assigned on my demon form spirit tab.