Looping the Loop - my delinquent Cessnas

My GA aircraft have a bad habit. When ATC tell them to exit at the next available taxiway they immediately turn off the runway, do two 360 ground loops, go back on the runway briefly and then head off across the grass to their parking spaces. Now... this is beyond a joke. Its not that they misbehave all the time - they are totally obedient at take-off, following the nodes and links perfectly. Any explanations? Any solutions?