Playing since retail release of prophecies, I remember henchies often got stuck, rez'd in superfast attack mode so they could die again, hid underground, and sometimes would fly!
As programs go, these AI's are pretty good. But there are still problems, even in Prophecies.
Helping another player couple weeks ago, I went into Griffon's Mouth from Kryta with my Ranger. My pet vanished! Then two henchies got stuck in the open tunnel for no good reason. Got them loose and the healer got stuck. We both got disgusted and quit.
If you're going to play with henchies a lot, monk is a good secondary. Keep the healer hench alive and all will go well and you will probably not die. Depend on the healer hench to keep itself alive and you will be sorry.
Best way to pull with henchies is to back up with henchies in front of you until you attract the attention of the mobs you want, then run a good long way. Using a bow is really dicey.