I've had similar experiences when doing enemas. I wouldn't get too worried about that fact in particular. You've got to remember, when you do an enema, you're flushing out food that's pretty far up in your digestive tract. It's only natural that you're going to wind up seeing some vegetable fiber still intact.
The fact that you don't see this undigested fiber in your normal no-enema stool should be a good sign, as it means it's getting digested at some point.