First day flying at Redhill a couple of years ago, I was gutted to listen in on the tower freq and get all excited at the impending flyby of "Mustang XX" only to find out that it belonged to a bloody R-22! It's the helicopter training school callsign.
I have heard that call sign at Manston before and same as you was abit upset that it was only a robbo, not that there's anything wrong with them.