I had a problem with a Res'd Rak'Sheen -- after I left the dark forest he didn't attack anything any longer. He would follow me but stop if there was an enemy nearby. The baddies would not attack him although they'd hover around for a bit. As soon as I was out of range of the critters or if they were killed then Rak'Sheen would fly back to me. Also, it was impossible to banish him. So he annoyingly followed me around for the rest of the game, unable to help or be hurt. This was very frustrating in small quarters where he would obscure things I needed to click on. Of course I could press Alt to resolve some of the problems but it was maddeningly annoying.
Just wondering if anyone else has run into this problem. Maybe he ran out of Mana? But that doesn't explain why I couldn't banish him and why he wasn't ever attacked.