My 13 Week old Shiba puppy is peeing on floor?

Before I even start asking the question let me state that my puppy has been using his wee wee pad tray successfully for almost a 3 weeks now without any accidents.he practically potty trained himself. I was very pleased with his behavior but since yesterday he has developed an odd behavior.every time he needs to pee/poop he will go to his tray and step on it with his front paw ( in any direction) and then he would deliberately pee /poop on the floor. Right next to his tray ( the very edge) its very strange cuz he is going to the tray then he sniffs it like then he position himself on the very edge and while his front paws ares till on the tray he would pee/poop on the edge on the floor. I even tried saying NO!!! and cleaning it right away, and trying to put him on tray. Yet he continues to do so, it is very strange cuz he never did it before he always went on the pad even if it was soiled, and now I change his pads quickly because I thought he may not wanna use it even after only peeing on it once, yet he continues to pee/poop on the floor while standing on the tray, it's really frustrating, what to do?? I really want to change this behavior without any strict punishment because after all he is a puppy even if I scold him he wont understand it. Advice please!