I had almost this exact same experience when teaching an algorithms course. I had to stop giving automated feedback when I had a student turn my own code back i

I had almost this exact same experience when teaching an algorithms course. I had to stop giving automated feedback when I had a student turn my own code back into me and then lie to my face when confronted about it. It only took 3 weeks. The worst part was how bad I felt for taking something useful away from the students who weren't abusing it.