This isn't a bug. I am willing to bet every time you have been detected, it has been by a robot. They have some special ability that increases their range and detection of stealth-ed players. Even the Sentinels Aggro Dump will pull them. Normal Humanoid mobs will not adhere to this. As far as the droids go in LI, that is also a mechanic. Just because you are a stealth class, it does not mean you get a free pass
Welcome to the land of normal classes.