#1 - Oct. 12, 2011, 12:26 p.m.
When I was playing on my DH, I hit level 10 and at first selected Thrill of the Hunt as my passive. Later, I switched it to Brooding for a short period and then went back to Thrill of the Hunt. While I had Thrill of the Hunt selected, the Brooding buff stayed above action bar. I wasn't able to test if it still worked in terms of healing me, because I was never injured. I'd assume its only a visual bug though, but obviously thats speculation.
The buff icon went away around when I entered the Skeleton King's room. I don't know exactly when, but I noticed it was gone while fighting Leoric.
http://img35.imageshack.us/img35/4926/screenshot20111012at111.png