I had a Miami Center Tracon controller do this to me once. It was a busy freq at the moment, so I was just responding with the flight number vs full call sign. I did it again another time or two inadvertently. Again. We were busy, He was busy. Then he screamed at me to say "full call sign." So I did from there on out. Do controllers have "checks" like pilots do? I was assuming that he was on a "check ride" with his agency. So I didn't push back. He was just trying to do the right thing.