I don't understand why some people do not believe this can happen without cheating. The PS2 runs based on numbers in hex and binary, so numbers can be truncated accidentally if anything weird happens to the system. Why do PCs screw up all the time? Why is the sky blue? Why does the positraction on the rear-end of a Plymouth work? It just does.
While playing Rallisport Challenge 2, I saved my replay because I had a spectacular crash. When I went back to watch the replay, after my crash my car just turned towards the wall of the tunnel, got stuck, and just sporadically accelerated into the wall. I was pretty pissed because I didn't get to see the second crash. After some time (a few days), I went back and watched the replay again, and it went through the whole thing as if nothing happened. Things screw up. It happens. Same thing goes with Tekken 4 and it's recording process for juggles in the game. Sometimes it records different things than what you inputted for your moves. Anyway, the PS2 isn't perfect, and maybe... just maybe.. PD's code could have random errors for particular events.
By the way, your DS2's button may not be going bad. Sometimes the rubber pad that rests on the sensor can get misaligned and cause problems. My D-Pad started cutting out (probably from getting pissed and chucking the controller at something), and I had to take it apart recently because I got tired of it not working - especially during racing. Turns out I had moved the position of the motors as well and that's why they weren't working properly, and once I just reassembled it (just place everything in its original spot again - very easy), the controller worked like new.