When casting sandblast, there is a small delay between the start of the animation and the spawn of the projectile.
During an aram-match as chromie against Anub’arak it happened multiple times that I got stunned during that windup-animation. Shortly after being stunned, the projectile was cast and I received stacks for the quest (‘Once Again the First Time’). Because I was stunned before the ability was cast, the cooldown for sandblast was also reset, allowing me to cast it twice in quick succession.
I remember this happening before i picked the talent which grants cooldown reduction on long range hits.
It’s not a bug. Most of abilities CD sets to 0 sec if its cast is interrupted.
But the cast was not interrupted.
Sandblast fires regardless of the stun and resets the cooldown even if the ability was cast