He didn't go on a tour (Spiritual Healing) in Europe with the rest of the band because of personal problems and if I'm not mistaken, he also left in the middle of the Human tour for some reason. I'm not sure about the last one. Also I've heard that he used to be a very hard person to work with (hence the multiple line-up changes in the beginning of his career) though I'm not sure of that either. Could be just people badmouthing him.
