I think it's working fine, I think I misunderstood something, my apologies. It wasn't clear to me that once you buy improved burst, the extra damage from mystic burst no longer triggers. I buying mystic burst without leveling the ability to the +80 damage, adding spirit from other items, but not achieving the threshold, which looked to me I was losing damage from mystic burst no longer triggering.
Sorry for inaccurate reporting, I just could figure out what cause the drop. Maybe there is a way (if it doesn't already exist) to let people know the improved ability, isn't additive to the base ability. Overall, might not be that important. Thanks for listening.