Deathstalkers mark not always applying from ambush? (Action Targeting bug)

Am I missing something? Is it not supposed to apply to your target from stealth/ambush on sin rogue? I just tested on 2 random mobs and they arent getting the debuff.

Is there a cool down between mobs?

I just tried it again, worked on 3 rando mobs next 2 it didnt then worked again. Its random. Anyone else seen this issue?

EDIT - I just figured it out. Its not applying sometimes when the enemy isnt targeted and Im relying on the action targeting to attack. So if I still have a dead enemy targeted and I sneak up and attack another enemy without changing to that one as my main target it doesnt apply.

Submitted to bug forums.