I was off healing in a Scenario last night and came across a bug I think.
I went oom throwing up some heals on the other 2 people and then one of them pulls the "boss" I hit Shamanistic Rage and then hit SS followed by Ascendance. Before Ascendance I was able to use SS but during Ascendance I noticed that I was not able to use Stormblast since I didn't have enough mana.
I proceeded to try to reproduce it after the Scenario and it did the same thing.