Dishonored Message Board  

Thanks for those links. They helped a lot. Also I found the answer to my own question. The only achievement affected is the Ghost one.
Now I'm only guessing here but I think its because the stealth option is doing something weird where its interrupting ai detection and your actually in a constant state of detection. The only reason I say this is because towers and pylons detect you no matter what the second you are in range. You can't even use actual stealth to get close.
But if you turn off stealth function you can get closer to them.

[Edited by Slimewaffle, 6/17/2015 5:15:45 AM]

I can confirm that the stealth option will not let you get the Ghost achievement. It is as Slimewaffle said: even though guards can't "detect" you, on level 2, a maid did see me and ran away from me. So I'm guessing you are not really 100% stealthy, it's more like you turn off the detection system or something like that.
Still a great editor/trainer, thanks for your work.