There was a long thread about this a year ago, about who had D on EN. A lot of people had D on EN. Some EN are only hydrolised whey, dried glucose and medium chain tri., it is highly bioavailable, and there is very little to form stool with to begin with. Especially 028 is very bioavailable, modulen and peptamen a bit less. D isn't normal, but D is very common on them because EN is 100% bioavailable unless they add fibers or other types of fats to them, but many EN don't.
The effectiveness of EN also doesn't seem to be lessened if you add regular food to EN, it doesn't appear to have to be exclusive to get the benefits from EN. I posted something about that a while ago. EN stimulates the release of cell adhesion molecules that bind to bacteria, it's going to do that regardless if it's exclusive or not, that's good for people who get too much D on exclusive EN. It's not been shown in vivo yet, but I don't think you need to be on exclusive EN to get all the benefits from EN.