Bugs... no, the code has been available for a long time and there should be no nasties there to cause what you are seeing.
Another likely cause of what you describe in your first post would be dodgy sensors. Try swapping the sensors left for right; does it spin the opposite way? If so one sensor is not working correctly.
With the 'bot on and supported check both sensors output in dark and light conditions with a volt meter. Do the outputs change? do they roughly match?