Ok, here's another data point.
[20:19] You start Sniper Blast.
[20:19] You activated the Sniper Blast power.
[20:19] HIT Infantry! Your Sniper Blast power had a 95.00% chance to hit, you rolled a 55.97.
[20:19] You hit Infantry with your Apocalypse: Chance for Negative Energy Damage for 107.08 points of Negative Energy damage.
The main damage did not take effect, but the proc from Apocalypse happened. Though with this, we got the HIT dialogue. So not sure if this is the exact same bug, but my theory is if the proc didn't happen, we would not have gotten the HIT and agro.