I was playing 0.5 and 1 starred songs tonight to improve on the accuracy and score of those that I had already played. Getting the accuracy up by a few percentage per song improved my accuracy for 1 starred songs all the time, but at one point I improved by a total of 15% in two songs and the total accuracy for 1 starred songs didn't go up at all even though my total total accuracy went up by 0.01%. This indicates a bug somewhere, since the improvements definitely should have even more effect on the 1 starred accuracy which is calculated from less songs than the total accuracy. (and it's not a caching bug or anything, I tested)
EDIT: Improved on another previously played 1 star song with 5%, still no effect.
EDIT: Improved on another previously played 1 star song with 5%, still no effect.