Once you activate a cheat, say Upgrade points, at the end of the wave (that's where I saw it) there is a red message @ top of screen saying CHEAT DETECTED.
I can replicate the "problem", but I don't personally see it as an issue. The Dev set it up so you can cheat, but not gain anything, like achievements. You would have to find the detection, which could be a check system of max possible credits, health, or even a redundant system to keep track of credits, which triggers the leaderboard lockout. This is the same effect as turning sv_cheats on in Portal 2
IMO, that is better than some form of lockout from the game, like a VAC ban. (I know, VAC is not in this game)
by the way, Great job on the trainers these past few days, can't believe how much you have done!