Occasionally, when I am in the hidden status and use Assassin's Blade, I successfully hit with the power but do no damage. The 'hit' sound effect plays, but no orange numbers show up and my target's health bar doesn't go down. Because the game considers it a hit, I am broken from stealth -- if I had missed, I would still be hidden, and I would simply be able to wait until Assassin's Blade has recharged and try again.
I'm curious if this is happening across the board on a more general basis, and this is just highly noticeable on Assassin's Strike-style powers due to the harsh penalty associated with hitting, breaking stealth, and doing no damage.
I'm pretty sure I had not been perceived and hit from stealth -- these were enemies where I was normally able to AS a boss or lieutenant with impunity, this only happened on a select mob in a mission.
I will post screenshots of the combat log if I recreate it while solo -- I was only able to glance at them before the rest of my team got moving, but I saw that the power use had an entry in the combat log where it rolled below the 95% I needed to hit, but there was no damage listed, which matches up with what I observed.