If you have a laser sight equipped on your gun and whenever you enter stealth mode you become invisible and laser sight gets turned off (unless aiming with the gun). Unfortunately sometimes your enemies are able to see your guns laser sight while you are stealthed - making it increadibly easy to locate you. From what I have noticed one of the things that seems to cause this problem is performing a ledge grab while you have stealth mode enabled.

I hope this is good section of the forums to post bugs in and that the issue will be adressed next patch