This isn't a bug. I am willing to bet every time you have been detected, it has been by a robot.
Nope, this applies to random mobs. The whole Ilum quest line were like that and I was "spotted" but non-robot characters.
Just because you are a stealth class, it does not mean you get a free pass
Welcome to the land of normal classes.
Well, the only difference with the stealther being way more squishy than any other "normal" class.
That's actually why we USE the stealth mode, otherwise it is pointless.
That "way too long range" of stealth detection is incorrect.
You can learn techniques to avoid it, but first moments are unpleasant and actually a BIG surprise. To you and to the group even more - as they cannot rely on your primary ability.