After you fail a challenge you get to choose a difficulty and a game mode (Race Setup), after pressing Cancel you return to main menu, if you proceed you get to choose a track and Singleplayer mode proceeds afterwards.
Can confirm on SuperTuxKart ver. 0.9.3.
Had it happening too. Annoying issue.
It only happens when the continue button is pressed quickly at the end of the race.
Most helpful comment
It only happens when the continue button is pressed quickly at the end of the race.