My pup used to chase shadows and she now does not. We used methods that I dislike and hope to never use again, but I believe it was necessary. One of her relatives is so obsessed with shadows that she will sit by a window all day waiting for a branch to cast a shadow on the floor; we did not want our pup to be like that. We used a choke collar and when she looked at a shadow, told her to leave it; if she did not, then we tightened then released the collar. That being said, after about one month of working on it about 2-3 hours a day, she is now back to normal and totally ignores shadows
I would suggest getting something like the gentle leader harness (attaches in front). You could use the method I stated above, but it will knock him off balance as opposed to choking him. I wish I had known about that harness when my pup was obsessed with shadows.
No, I believe that behavior is abnormal for any breed of dog. Hopefully some more experienced members will have more advice for you.