It seems the unlimited ammo even affects shootouts for me. I draw my weapon and we both just stand there unable to fire. The work around I've been using for this is to disable unlimited ammo just before the duel.
I guess you're wrong, BlutVampir. It has nothing to do with your speed. It doesn't take me longer when I don't start the trainer at that part of the game. It also doesn't have anything to do with the options you activate during the game. I started the trainer and the game and loaded chapter 2. I didn't activate anything and the "bug" still appears at the same place. The trainer seems to manipulate something no matter if you turn on any options or not. I guess it happens as soon as you press "F1".
Just play those two chapters where the bucket bug occurs without trainer and use the ingame cheat options via console instead.