I'm having fun with one at the moment - allegedly I climbed into a bit of CTA in speeds and climb rates of which the aeroplane I was flying was incapable, on a sortie where I had no reason to fly that high, whilst mode-S was squawking hex code but not reg. We checked the mode S a few weeks later with the same tower, and they could read reg and hex both - no maintenance done on same box in between.
I pointed out that it probably wasn't me for these reasons, and was subsequently the unhappy recipient of an email suggesting that I was not showing the right attitude and probably needed reporting to CAA for licencing action. Everybody can probably guess, without being told, the tone of my response to that.
I don't dispute that putting big and little aeroplanes in the same place at the same time is a bad thing unless properly controlled, but there's a distinct attitude problem in the airspace allocating community that is as much in need of fixing as anybody's navigation here. Also just possibly the technology isn't quite as good as NATS think it is at detecting these things.
G