When I have 3 stacks of Astral Fire and I cast Blizzard 3, if the spell miss or the target is invulnerable, then I lose the 3 fire stacks but I won't gain the 3 ice stacks. The same thing happens when I cast Fire 3 with 3 ice stacks.
But if you have 1-2 stacks of fire and cast a Blizzard 3 or vice versa, if the spell miss/target's invulnerable you won't lose your current stacks.
I've been noticing this a lot lately especially on fights where the boss temporarily becomes invulnerable such as Atomos and Thanatos on CT or Primals during their huge AOE cast (such as Ifrit's Hellfire).
What do you guys think? Is this working as intended or does the double dip supposed fix actually spawn another bug?