Could the time-to-revert when you change the antialiasing slider be increased?
Mine works fine when I go into settings from the main menu but when I try it after I have a track loaded (from the MP lobby or Esc Key menu) it times out before my computer's got it's act together. I get a brief glimpse of the "do you want to keep this setting" screen then it blacks out again and I have to wait for it to go back to the way it was before.
It's the same thing for me since the first time i played GPBikes.
Same here, even with a powerfull machine :/