i had this happen to me 4 times already.. a scorpian will spit acid at you untill you die but there is no scorpian. you have to move around to exit combat. the profile i was useing was the skinning in uldum so yall might want to watch out for this.
chances are its a bugged mob, some CC's handle them better then others. ive herd reports that people who report these to blizzard, a gm will remove the bad mob, and you can continue to bot happily, however that may very well be ill advised.