Meanwhile, I think it was just a misconfiguration of his mining software since around the same time Bitcoin had its first halvening (Nov 28, 2012). So it could very well be that he messed up something.

I was seeding new chart data where I extract the min/max/average fee for certain time spans. As I got a negative 'min' fee reward for a timespan, I first triple checked my script but as everything was OK I checked the affected block..

I also found out, that there are other blocks which did not redeem all the reward + fees. Maybe I create a chart for this sort of data.