If it's doing something it shouldn't, then submit a bug with the particulars. What is your stealth skill, is it happening when you were already stealthed or after you stealth while running away or using vanish, what is the relative level of the attacker, etc., etc. Without details it's just a complaint, not a bug.
yeah, have had the issue a few times too...you are in stealth vanish or normal for 5-10seconds and suddenly a pet hits you out... It's an active issue on the bugtracker though, so we will have to wait and see if they can fix it.