The thing you are taling is probably combat bug. It caught me many times since I began playing. try /reload ui it should help. Your char acts like it was in combat while it is not. You can't prowl, stealth, mount up.
This happened to me this weekend in wsg on my 90. i have no idea what caused it. It wasnt a combat bug though. I could mount and such. it was acting almost as if i had faerie fire. I could vanish and I want to say dying also reset it. No idea what caused it and I couldn't find anyone else who had the same problem
There was a bug a while back that if you got knocked out while stealthing, you gained your stealth buffs but would be out of stealth, as such the game recognised you in stealth stance and you can't restealth while stealthed.
i find this happens most when ever you are loaded into a new instance. I dont just mean dungeons but also battle grounds or new crz phases . if you shift or stealth as you change or load the instance / phase sometimes wow will have a spazz attack . not sure if it helps any but im close to 1k posts so i figured id throw in my experiences
It's CRZ. I'm not sure why or how, but it's not just a stealth bug.
There have been a number of times that I am unable to stealth, but also unable to mount on my druid or shaman. I get "You are shape shifted" error message.
EVERY time I have encountered this bug has been after I changed zones.