Power Sting Triggering Before Special Activation?

SupperHero4Sales

While playing within the Arena recently I managed to trigger Power Sting Ability with Yellow Jacket (Special Attack One) versus Mordo and I noticed that he was Power Stung when activating his Special Attack. I re-triggered Power Sting once more while he had below 25% Maximum Health and held up Block only to notice Mordo instantly lose all remaining Health but I did not see any Power Sting notification? Is this normal for any Champions with Power Sting or could it have been caused by something different? Is Power Sting Damage Increased based on the type of Special Attack activated?

SummonerNR

Your PowerSting will damage Damage opponent prior to the actual actions of opponent's SP 1/2.
So if the Sting is enough to kill opponent, it will. So he's dead and rest of his SP 1/2 doesn’t even take place.

FYI, an SP3 actually does take place though before any Sting Damage occurs. So with opponent's SP3, you will be hit with SP3 damage before your Sting will do it's damage to opponent.