Just another bug in the system. GT3 was rushed, for an early release, so there are a couple of them.
Another bug example is in the Run & Setting. First use a car to go around the track once, then stop to view the replay that starts right away after stopping. Then restart a new lap, but don't go as fast as the first time, then stop again and listen carefully at the second replay. You will here the wind effect, and transmission noise, of your previous car moving ahead of the replay of the car you just used, but you will not see anything but the second car.
I hope GT4 dosen't have as many bugs, even though the rumor is Sony is pushing PD for the game. In order to make the Christmas sales bonanza of course.