So I made a cleric today with the darkness/luck domains, and I had 3 darkness spells ready, yet when I put cure/inflict light wounds on my hotbar so that in an emergency I could spontaneously cast them, they were grayed out as if I didn't have any spells prepared there. My guess is that I'm casting as a wizard/sorcerer even though it's on the cleric spell list, and it isn't 'seeing' any spells there that can be exchanged for cure/inflict.
It's always been that way for domain specific spells, sadly. If there is a fix, awesome, but I don't believe there is.
Domain spells can't be used for spontaneous casting. I think this is a D&D rule anyway...
By the rules:
QuoteRules- Must serve a patron deity. Upon character creation, players must enter a name of a deity in the “Deity” field, choose an alignment associated with their character's god, and select two domains available to clerics of said deity. Clerics that do not have a deity, are of an incompatible alignment, or choose improper domains for their deity will be unable to cast divine spells or receive domain abilities.
I don't know of any god who has both the Luck and Darkness domains, so perhaps this is where the problem lies?
Scratch that, found one that does....who I won't name.