They probably made this fix to counter the double flare glitch. Not because they thought the previous mechanic was OP.
But it looks amateurish.

Why ? Because:
Buff Astral Fire 3: Cast Blizzard 3. AF3 is removed 0.5sec before the end of the cast.
Buff Astral Fire 1: Cast Blizzard 1. AF1 is only removed when your spell hits the target.
Buff Astral Fire 1: Cast Blizzard 3. AF1 is only removed when your spell hits the target.

Amateurish fix is amateurish.