I have been experimenting with various builds to try to find a competitive DK healer build for veteran trials. I wanted to try using my Perfected Asylum's restoration staff as a means to help offset the relatively high cost of DK skills, particularly Cinder Storm which is about 4.6k magicka, even with 6 piece light armour. However, when I checked to see what the skill cost was after I cast combat prayer, it was unchanged. I see no reason why this skill shouldn't benefit from the reduced cost effect of the Asylum's resto so I assume this is a bug. I have not had the chance to check the unmorphed skill or a non-perfected staff yet.