This is what I did to reproduce the bug after deleting the prefs.ini file to fix the problem.
- Start new game and select a xml mod race.
- After new game is created, exit game.
- Clear mod folder.
- Start game, hover on Quick Start which reads unavailable.
- Start new game and select a stock race.
- Game will start with a random race.
- Go to Main Menu and select New Game.
- Selected stock race is still selected but when you go the opponents window the player is set to random.
You can fix this by going to prefs.ini where you will find that Player0Random=1 when it should read Player0Random=0.
The upside is that if you ever want to start as a random player you can go to prefs.ini and set Player0Random=0 to Player0Random=1.