Hello Howard,
Thank you for your kind reply. That makes sense to me! The issue kept me awake the last couple of days, never realised it was solved this way. That also answers the question whether it is important were at the car the transponder is located. I think I undersood: In the first lap, the car crossed the loop. The timing software registrates the Peak_signal_time and the first lap starts for that car. Not important were the transponder is located, it is at the same location the next lap. The car will cross the loop a second time and again the Peak_signal_time is registred for that car. The time_difference in Peak_signal_time is the lap_time.
For spectators at the side it is thus difficult to judge if two cars in the end of the race have done the same amount of laps and cross the loop visually at exact the same time (by eye...); It depends were the car's transponder was (more to the front or rear), but the electronic timing will show the difference in time of both cars. The car that had the transponder a bit more to the front started the lap earlier as well, it is the lap_time that counts. I think I all understand now.

@hpikllr: I think after reading the explanation by Howard, we better not bet the $1000...

Thanks Howard!